Rep. Duncan Hunter, R-Calif., sent a letter of resignation to House Speaker Nancy Pelosi, D-Calif., and California Gov. Gavin Newsom on Tuesday, and plans to officially leave his post on Jan. 13.

Hunter, 42, pleaded guilty last month to a single count of conspiracy to misuse at least $150,000 in campaign funds for personal expenses. Hunter initially maintained his innocence for months but ultimately reversed gears and struck a deal with prosecutors. He is facing up to five years in prison and will be sentenced on March 17.

In his letter, Hunter didn't once mention his guilt or innocence and omitted any details of his plea bargain. Instead, he championed his congressional accomplishments and focused on his military service.

Hunter opened the letter by describing his decision to join the Marines following the 9/11 terror attacks, before listing the ways he's helped his constituents better their lives.

"I learned from an early age the importance of liberty, the value of patriotism, and what a strong and secure border can bring to a community," he said. "During my time in Congress, I had the privilege of helping thousands of individuals in my district."

REP. DUNCAN HUNTER, IN REVERSAL, PLEADS GUILTY IN CAMPAIGN FUNDS CASE

"Perhaps the contribution I am most proud of is giving a voice to our men and women in uniform," Hunter added. "I will always be proud to stand with the men and women who protect our freedoms."

According to the indictment, Hunter and his wife spent part of the campaign funds on a birthday party for their daughter at an expensive hotel, along with funding social outings with friends at a French bistro in Washington, D.C.

Prosecutors also accused Hunter of spending part of the money on extramarital affairs with lobbyists and congressional aides.

Hunter's wife, Margaret, was also charged in the case but accepted a plea deal in June, which required her to testify against her husband. The couple could have faced up to decades in prison prior to their plea agreements.

Republicans enjoy an 11-point registration advantage over Democrats in California's 50th District. Former congressman for California’s 49th District, Rep. Darrell Issa, is considered one of the front-runners to fill the vacant seat.

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Newsom, a Democrat, has yet to announce if he will call for a special election; he has the option under state law to leave the seat vacant until November, according to The San Diego Union-Tribune.

Fox News' Andrew O'Reilly and Morgan Phillips contributed to this report