The two-time Emmy-winning actor will make his debut on the CBS sitcom in the May 12 season finale.
The character is described as an anthropologist and he was not affectionate at all toward his son, reported Ace Showbiz.
The show's producers announced Hirsch's casting at PaleyFest.
Galecki revealed that he's the one who invited Hirsch to play his on-screen father when he met the veteran actor at NBC's James Burrows tribute recently.
"We're all honored to be invited to this James Burrows tribute ... And we all had the opportunity to meet these incredible casts Jimmy directed and I had the opportunity to meet Judd Hirsch," Galecki said.
"..Not because I wanted to base Leonard on his character but the purpose his character served - this anchor in this group of people - and he was just as much at times a voice of reason as he was just as confused as everyone else."
"I shared that with him and a lightning bolt struck ... or another merlot ... And I said, would you have any interest in playing my dad on the show?" he said.