McKellen, 74, told Jonathan Ross back in March that he was "going to marry Patrick."
"Well, no. How else do you put that? I am going to officiate at his wedding," the "X-Men" star said at the time.
Both Stewart and McKellen acknowledged the wedding on social media. Stewart tweeted a photo of himself and his new bride drowning in a ball pit.
Yes, married. pic.twitter.com/ZSMnpluSeL— Patrick Stewart (@SirPatStew) September 8, 2013
"I did my part," he wrote.
Stewart, 73, met his 35-year-old wife at the Brooklyn Academy of Music in 2008. This is his third marriage.