Kelly, who has been on personal leave since Jan. 8 to care for his critically wounded wife, will resume training Monday in preparation for commanding the shuttle Endeavour, set for launch April 19 on a mission to the International Space Station, a NASA release said Friday.
"We are glad to have Mark back," said Peggy Whitson, chief of the Astronaut Office at NASA's Johnson Space Center in Houston. "He is a veteran shuttle commander and knows well the demands of the job. We are confident in his ability to successfully lead this mission, and I know I speak for all of NASA in saying 'welcome back.'"
Kelly said he made the decision to rejoin the crew as mission commander after he was convinced his wife was improving consistently.
"Things fell into place and she improved very fast, so the decision became easier over time," Kelly said. "I know my wife very well and I know what she would want, so that makes the decision easier."
He added: "I am looking forward to rejoining my STS-134 crew members and finishing our training for the mission. We have been preparing for more than 18 months, and we will be ready to deliver the Alpha Magnetic Spectrometer to the International Space Station and complete the other objectives of the flight."
Earlier Friday, Sen. Bill Nelson, D-Fla., who has flown a shuttle mission, told CBS News, "If Gabby (Giffords) had the decision to make, she would tell her husband, 'Go ahead and go fly."'
Kelly's twin brother, Scott, is at the space station in command of the team there.