Retired astronaut Mark Kelly announced Tuesday that he is running to finish the late Sen. John McCain's last term representing Arizona, which ends in 2022.

Kelly is the husband of former Rep. Gabby Giffords, who survived being shot in the head in a 2011 mass shooting that left six dead in Tucson, Arizona. Since that attack, Giffords and Kelly have been prominent advocates for gun control.

He is the first Democrat to enter the field ahead of 2020 and is widely seen as a formidable candidate, given his biography and likely ability to raise the millions of dollars needed to take on the GOP's established candidate, Sen. Martha McSally.

McSally, who formerly served in the House, was appointed to the seat by Gov. Doug Ducey after she narrowly lost her campaign for Arizona's other Senate seat to Democrat Kyrsten Sinema in the 2018 midterm election. She is considered one of the most vulnerable Republican senators heading into the 2020 election.

Profile:Seven years after shooting that changed everything, Kelly still working on what comes next

McSally is a former Air Force pilot and was the first woman to fly combat missions. Kelly was a pilot in the Navy.

Both veterans will fight to fill the seat of a legendary Navy pilot who was shot down and held as a prisoner of war by North Vietnamese communists for five and a half years.

Kelly's announcement comes a few days after former attorney general Grant Woods – a Republican who joined the Democratic Party and is a fierce critic of President Donald Trump – announced he would not be getting in the race. Democratic Rep. Ruben Gallego is also considering a run for the seat.

Kelly announced his candidacy in a video he shared on social media that largely focused on his biography and his marriage to Giffords.

"You know, I thought then that I had the risky job," the former astronaut tells his wife as they discuss her shooting. "Turned out that you were the one who had the risky job."

He credited his wife for giving him the drive to run for the Senate.

"I learned a lot from being an astronaut. I learned a lot from being a pilot in the Navy. I learned a lot about solving problems from being an engineer. But what I learned from my wife is how you use policy to improve people's lives," he said.

"I care about people. I care about the state of Arizona. I care about this nation," he said. "So, because of that, I've decided that I'm launching a campaign for the United States Senate."

The video ends with Kelly and Giffords sitting on a couch, "Damn the torpedoes," he says.

"Full speed ahead," they say together.

He received a degree in marine engineering and nautical science from the U.S. Merchant Marine Academy, graduating with highest honors in 1986, according to his biography with NASA. He also has a master’s degree in aeronautical engineering.

During his military career, Kelly picked up awards ranging from the Distinguished Flying Cross to the NASA Exceptional Service Medal. He flew 39 combat missions in Operation Desert Storm and logged more than 5,000 hours in 50 different aircraft, NASA reported.

Kelly announced his retirement from NASA in June 2011, five months after Giffords was shot. He co-founded Americans For Responsible Solutions, a gun-control organization.

Contributing: Ronald J. Hansen, Arizona Republic