McCallum, 30, is 6-foot-3 and was a second round pick (No. 36) by the Kings in the 2013 draft. He spent his first two NBA seasons with Sacramento, followed by stints with the Spurs and Grizzlies.
He has has also played for Reno, Austin, Grand Rapids, Agua Caliente and Greensboro of the G League, including time with the Swarm in the G League bubble last season.
“I am now in my ninth year as a professional, my fifth season overseas — I would like to use the many experiences and bring them here to Hamburg,” McCallum said in a statement. “The team is relatively young, so as a veteran I have to be able to take on responsibility.”
McCallum has also spent time in Turkey, Spain and China.