A former fighter pilot and Nasa astronaut who has flown 20 million miles in space is a top contender to become Kamala Harris’s running mate.

Mark Kelly, 60, the Arizona senator, has a record of beating candidates endorsed by Donald Trump in the vital battleground state where Ms Harris is trailing her Republican rival.

He has commanded shuttle missions on the Discovery and Endeavour and flew 39 missions as a US navy pilot during the Gulf War before retiring to care for his wife who was shot in the head in an attempted assassination.

Democrat strategists told The Telegraph that Mr Kelly, who has a strong record on immigration, would be a “formidable choice” for Ms Harris and could help prop her up in her weaker areas.

Mr Kelly was among the potential vice-presidential candidates Ms Harris called after President Joe Biden stepped down as the Democrat candidate.

An official vetting process then began and ABC reported that Mr Kelly and Josh Shapiro, the Pennsylvania governor, were the two leading contenders for the role.

Born and raised in New Jersey to two police officers, Mr Kelly’s mother became the first female officer at the West Orange Police Department.

Mr Kelly attended the United States Merchant Marine Academy before becoming a navy pilot. During his air force career, he was deployed several times on the aircraft carrier USS Midway and flew 39 combat missions in Operation Desert Storm.

He spent more than 50 days in space, travelling more than 20 million miles, after he and his identical twin brother, Scott, were selected as astronauts in the same Nasa class in 1996.

He retired from Nasa in 2011 after commanding Space Shuttle Endeavour on its final flight and after his wife, the former US representative wife Gabrielle Giffords, survived an assassination attempt in 2011.

Six people were killed in the attack in a supermarket in Tucson and Mr Kelly dedicated himself to helping Ms Giffords, who was left disabled after she was shot in the head.

The couple became vocal gun control advocates, starting gun control non-profit Giffords to call for stricter laws.

Mr Kelly entered politics in 2020, winning a difficult senate race to fill John McCain’s seat.

He was re-elected two years later, beating Republican Blake Masters, who had been endorsed by Trump, by more than 125,000 votes.

While Ms Harris has already been attacked by the Trump campaign as the “border tsar”, Mr Kelly was a vocal critic of some of Mr Biden’s policies such as reversing the Trump-era Title 42.

Mr Kelly also has a strong record for abortion. He pushed for access for women in Arizona, which has a 15-week ban.

Democrat strategist Jason Oritz said: “He’s run tough races in a tough state.”

He said that while Trump had selected JD Vance, who double’s down on the former president’s views, Mr Kelly would “differentiate the ticket” adding “a centrist Democrat from a purple state where Democrats need help”.

He said the Republicans “should be very nervous” about the potential running mate.

The Arizona senator was also described as the “smartest selection” by Washington Post columnist Karen Tumulty.

Mr Kelly has so far avoided questions about taking the job.

He told ABC News: “This is not about me. I’m going to be focused on doing everything I can to make sure she is elected because we cannot have a repeat of what we saw between 2016 and 2020.”