TVGuide.com reported Tuesday Garber was candid about his relationship when asked about his sexuality by blogger Greg Hernandez.
"I don't really talk about it, but everybody knows," Garber said, adding Andreesen is "going to be out here with me for the SAG Awards" this month in Los Angeles where his new show "Deception" is taped.
TVGuide.com said Garber previously confirmed his relationship to the Canadian magazine Forever Young Information last April, but the media didn't pick up on it.
"My companion Rainer Andreesen and I have been together almost 13 years in Greenwich Village. We both love New York," Garber told the publication.
Garber's credits include the films "Argo" and "Titanic," as well as the TV series "Alias."