Mark Kelly had taken a leave from training after Giffords was shot in the head during a mass shooting in Tucson, Ariz. On Jan. 8 Six people were killed and 12 others were injured.
Giffords is currently undergoing rehab in Houston.
Kelly has flown three times aboard space shuttles; April's trip aboard Endeavour to the International Space Station will be his fourth.
The mission already was set to be one of the highest profile shuttle flights ever. It will be Endeavour's last voyage and the next-to-last for the entire 30-year shuttle program, and will feature the delivery of an elaborate physics experiment by a Nobel prize winner.
The Associated Press contributed to this story.