Former CIA Acting Director Michael Morell announced his resignation Thursday as a senior fellow at the Harvard Kennedy School of Government over its hiring of Chelsea Manning as a visiting fellow.

"Unfortunately, I cannot be part of an organization — the Kennedy School — that honors a convicted felon and leaker of classified information, Ms. Chelsea Manning, by inviting her to be a Visiting Fellow at the Kennedy School's Institute of Politics," Morell wrote in a letter to the school's dean, Douglas Elmendorf.

"Ms. Manning was found guilty of 17 serious crimes, including six counts of espionage, for leaking hundreds of thousands of classified documents to Wikileaks, an entity that CIA Director Mike Pompeo says operates like an adversarial foreign intelligence service," Morell wrote.

14 PHOTOS Former CIA Director Michael Morell See Gallery Former CIA Director Michael Morell Former Deputy Director of the Central Intelligence Agency Michael Morell, who was interviewed for 'The Spymasters,' a CBS/Showtime documentary, about directors of the CIA, Washington, DC, June 30, 2015. (Photo David Hume Kennerly/Getty Images) Michael Morell, former deputy director of the Central Intelligence Agency, right, and his wife Mary Beth Morell arrive for a morning session during the Allen & Co. Media and Technology Conference in Sun Valley, Idaho, U.S., on Thursday, July 9, 2015. Billionaires, chief executive officers, and leaders from the technology, media, and finance industries gather this week at the Idaho mountain resort conference hosted by investment banking firm Allen & Co. (David Paul Morris/Bloomberg via Getty Images) Michael Morell, former director of the Central Intelligence Agency, attends the annual Allen & Company Sun Valley Conference, July 6, 2016 in Sun Valley, Idaho. Every July, some of the world's most wealthy and powerful businesspeople from the media, finance, technology and political spheres converge at the Sun Valley Resort for the exclusive weeklong conference. (Photo by Drew Angerer/Getty Images) Former Mossad Director (2011-2016) Tamir Pardo and former US Central Intelligence Agency Acting Director Michael Morell discuss 'ISIS, Israel, and Spymasters: A Reality Check' at the Harvard University Kennedy School of Government Institute of Politics John F. Kennedy Jr. Forum on May 3, 2016 in Cambridge, Massachusetts. (Photo by Paul Marotta/Getty Images) With a copy of a 'talking points' memo behind him, former Deputy CIA Director Michael Morell testifies before the House Select Intelligence Committee April 2, 2014 in Washington, DC. The committee heard testimony on the topic of 'The Benghazi Talking Points and Michael J. Morell's Role in Shaping the Administration's Narrative.' (Photo by Win McNamee/Getty Images) Leon Panetta, outgoing Secretary of Defense; nominee for Secretary of Defense, Sen. Chuck Hagel, (R-NE); President Barack Obama; John Brennan nominee for Director of CIA, and Michael J. Morell, acting Director of the CIA, are shown during a press conference in the East Room at the White House in Washington, D.C., on Monday, January 7, 2013. (Photo by Nikki Kahn/The Washington Post via Getty Images) Michael Morell (L), former acting director of the CIA, and Michael Vickers, former Defense undersecretary for intelligence, listen to questions during a House Armed Services Committee hearing on Capitol Hill, January 12, 2016 in Washington, DC. The committee was hearing testimony the from an outside view on the U.S. Strategy for Iraq and Syria and the Evolution of Islamic Extremism. (Photo by Mark Wilson/Getty Images) Former Deputy CIA Director Michael Morell is sworn in prior to testimony before the House Select Intelligence Committee April 2, 2014 in Washington, DC. The committee heard testimony on the topic of 'The Benghazi Talking Points and Michael J. Morell's Role in Shaping the Administration's Narrative.' (Photo by Win McNamee/Getty Images) Michael Morell (L), former acting director of the CIA, and Michael Vickers, former Defense undersecretary for intelligence, look over their papers before the start of a House Armed Services Committee hearing on Capitol Hill, January 12, 2016 in Washington, DC. The committee was hearing testimony the from an outside view on the U.S. Strategy for Iraq and Syria and the Evolution of Islamic Extremism. (Photo by Mark Wilson/Getty Images) Former Deputy CIA Director Michael Morell arrives for testimony before the House Select Intelligence Committee April 2, 2014 in Washington, DC. The committee heard testimony on the topic of 'The Benghazi Talking Points and Michael J. Morell's Role in Shaping the Administration's Narrative.' (Photo by Win McNamee/Getty Images) Eric Jaffe, Head of New York Research at GLG and Michael Morell, former acting director of the CIA visit GLG (Gerson Lehrman Group) on March 4, 2016 in New York City. (Photo by Donald Bowers/Getty Images for GLG) Acting CIA Director Michael Morell is seen November 28, 2012 in the Senate Visitors Center of the US Capitol in Washington, DC. (MANDEL NGAN/AFP/Getty Images) Acting CIA Director Michael Morell leaves the closed Senate Intelligence Committee meeting on Capitol Hill in Washington November 15, 2012. A computer used by Paula Broadwell, the woman whose affair with CIA Director David Petraeus led to his resignation, contained substantial classified information that should have been stored under more secure conditions, law enforcement and national security officials said on Wednesday. (REUTERS/Jose Luis Magana) US President Barack Obama (2nd L) shares a laugh with his nominees for US Defense Secretary Chuck Hagel (L), current US Defense Secretary Leon Panetta (2nd R) and Acting Director of the CIA Michael Morell (R) during an event at the White House in Washington on January 7, 2013. (JIM WATSON/AFP/Getty Images) Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

Morell stressed that he does not take issue with Manning's gender identity and is against President Trump's ban on transgender service members.

"It is important to note that I fully support Ms. Manning's rights as a transgender American, including the right to serve our country in the U.S. military," Morell wrote. "But it is my right, indeed my duty, to argue that the School's decision is wholly inappropriate and to protest it by resigning from the Kennedy School."

Manning wasn't the only person announced as a visiting fellow this week. Harvard said former White House spokesman Sean Spicer also had been appointed.

12 PHOTOS Chelsea Manning See Gallery Chelsea Manning ABC NEWS - ABC News' 'Nightline' co-anchor Juju Chang sits down with Chelsea Manning for the first exclusive television interview since Manning's prison release. The interview will air on an upcoming special edition of Nightline, 'Declassified: The Chelsea Manning Story.' (Photo by Heidi Gutman/ABC via Getty Images) CHELSEA MANNING U.S. soldier Chelsea Manning, who was born male but identifies as a woman, imprisoned for handing over classified files to pro-transparency site WikiLeaks, is pictured dressed as a woman in this 2010 photograph obtained on August 14, 2013.Courtesy U.S. Army/Handout via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY. EDITORIAL USE ONLY NEW YORK, NY - JUNE 25: Chelsea Manning and Gavin Grimm ride with the ACLU in the 2017 Pride March on June 25, 2017 in New York City. (Photo by Taylor Hill/WireImage) People hold signs calling for the release of imprisoned wikileaks whistleblower Chelsea Manning while marching in a gay pride parade in San Francisco, California June 28, 2015. Manning has appealed to an Army court to overturn her court-martial conviction, a court filing released on Thursday said. REUTERS/Elijah Nouvelage/File Photo A placard showing Chelsea Manning and Edward Snowden photos is seen during the Easter March for Peace in Roemerberg, Frankfurt, Germany, 06 April 2015. Some 2000 demonstrators gathered before the City Hall to advocate for peace, under the motto 'Stop war and war propaganda - Solve conflicts peacefully'. Thousands have gathered to participate in over 80 events for peace during the Easter period in Germany. (Photo by Horacio Villalobos/Corbis via Getty Images) ODEONSPLATZ, MUNICH, BAVARIA, GERMANY - 2015/10/10: Demonstrators gather to protest against surveillance especially by the NSA. Amnesty International demands Obama to hand over his peace Nobel Price to Chelsea manning. (Photo by Michael Trammer/Pacific Press/LightRocket via Getty Images) U.S. Army Pfc. Bradley Manning is escorted out of a courthouse during his court martial at Fort Meade in Maryland, August, 20, 2013. Manning, 25, the soldier convicted of giving classified U.S. files to WikiLeaks, could face as up to 90 years in prison for giving more than 700,000 classified files, battlefield videos and diplomatic cables to the pro-transparency website. Prosecutors asked for 60 years, while the defense asked the judge not to rob him of his youth. REUTERS/Jose Luis Magana (UNITED STATES - Tags: POLITICS CRIME LAW MILITARY) Demonstration for Chelsea Manning in London, England, United Kingdom. Chelsea Manning (born Bradley Edward Manning) is a United States Army soldier who was convicted by court-martial in July 2013 of violations of the Espionage Act and other offenses, after disclosing to WikiLeaks nearly three-quarters of a million classified or unclassified but sensitive military and diplomatic documents. Manning was sentenced in August 2013 to 35 years imprisonment, with the possibility of parole in the eighth year, and to be dishonorably discharged from the Army. Manning is a trans woman who, in a statement the day after sentencing, said she had felt female since childhood, wanted to be known as Chelsea, and desired to begin hormone replacement therapy. From early life and through much of her Army life, Manning was known as Bradley; she was diagnosed with gender identity disorder while in the Army. (photo by Mike Kemp/In Pictures via Getty Images) Demonstration for Chelsea Manning in London, England, United Kingdom. Chelsea Manning (born Bradley Edward Manning) is a United States Army soldier who was convicted by court-martial in July 2013 of violations of the Espionage Act and other offenses, after disclosing to WikiLeaks nearly three-quarters of a million classified or unclassified but sensitive military and diplomatic documents. Manning was sentenced in August 2013 to 35 years imprisonment, with the possibility of parole in the eighth year, and to be dishonorably discharged from the Army. Manning is a trans woman who, in a statement the day after sentencing, said she had felt female since childhood, wanted to be known as Chelsea, and desired to begin hormone replacement therapy. From early life and through much of her Army life, Manning was known as Bradley; she was diagnosed with gender identity disorder while in the Army. (photo by Mike Kemp/In Pictures via Getty Images) ABC NEWS - ABC News' 'Nightline' co-anchor Juju Chang sits down with Chelsea Manning for the first exclusive television interview since Manning's prison release. The interview will air on an upcoming special edition of Nightline, 'Declassified: The Chelsea Manning Story.' (Photo by Heidi Gutman/ABC via Getty Images) CHELSEA MANNING NEW YORK, NY - JUNE 25: Chelsea Manning and Gavin Grimm ride during the 2017 Pride March in the West Village on June 25, 2017 in New York City. (Photo by Taylor Hill/WireImage) ABC NEWS - ABC News' 'Nightline' co-anchor Juju Chang sits down with Chelsea Manning for the first exclusive television interview since Manning's prison release. The interview will air on an upcoming special edition of Nightline, 'Declassified: The Chelsea Manning Story.' (Photo by Heidi Gutman/ABC via Getty Images) JUJU CHANG, CHELSEA MANNING Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

"Broadening the range and depth of opportunity for students to hear from and engage with experts, leaders and policy-shapers is a cornerstone of the Institute of Politics," Bill Delhunt, acting director of the institute, said. "We welcome the breadth of thought-provoking viewpoints on race, gender, politics and the media."

Manning, a former Army intelligence analyst, was convicted of leaking a trove of military intelligence records and spent seven years in prison before President Barack Obama commuted her sentence in January.

Manning is appealing her conviction, and the lawyer handling her appeal, Nancy Hollander, disputed Morell's claims that Manning's actions had put the nation in danger.

"There's a quote from Secretary of Defense Gates about how people don't work with the U.S. because they like us or because they trust us, but because they fear us and respect us," she said in a phone interview, referring to Robert Gates, who led the Pentagon under Presidents George W. Bush and Barack Obama. "So maybe at most, the U.S. was embarrassed. They never identified a single person who was harmed."

Hollander said Manning's appointment at Harvard was "terrific for Chelsea and for Harvard and for the students."

"Of course she's not posing harm to anybody anywhere," Hollander said. "She did a public service."

The Harvard Kennedy School did not immediately return a request for comment on Morell's resignation.