Kelly told the story of his family's history, including his mother's achievement of becoming one of the first female police officers in West Orange, New Jersey, his own achievements in space and with the U.S. Navy, as well as his wife's survival when an attempt was made on her life by an active shooter in 2011.
Democrats are eagerly watching the Arizona contest, having already beaten McSally once.
"I care about people".
"We're going to need to bring people together from all parts of the state and all walks of life. So because of that, I've decided I'm launching a campaign for the United States Senate".
Former Arizona Attorney General Grant Woods, a lifelong Republican who became a Democrat and a fierce critic of Trump, announced last week that he won't run, saying he didn't want to fight in a contested Democratic primary. John McCain's Arizona Senate seat in 2020 to finish the term.
McSally was chosen to take over the remainder of the term that Jon Kyl had temporarily filled.
Currently, that seat is held by Republican Martha McSally, who was appointed by the Republican Arizona Governor, Doug Ducey, after Mr McCain's death. The seat will be on the ballot again in 2022 for a full six-year term.
USA congressman Ruben Gallego of Phoenix is also considering a Senate run, which would likely set up a tough fight for the Democratic nomination.
Kelly will be competing against Republican candidate Martha McSally.
McSally, a former Air Force pilot, is expected to run as well.
Kelly also formed a gun control group called Veterans Coalition for Common Sense with retired Gen. David Petraeus in 2016. He and his wife formed Giffords, formerly known as Americans for Responsible Solutions, in 2013 "to prevent gun violence".
They have both said they support the Second Amendment but something had to be done to keep "guns out of the hands of unsafe people ..."
Though vocal in his politics, he has never held elected office before.
Kelly participated in four space shuttle missions, and before that, had served in the navy as a pilot, including in the Gulf War in 1990-91.