Killam took to Instagram to share the tribute, alongside a stunning black-and-white photo of his ladylove, who stars as Joanna Lyppiatt in the Noel Coward comedy Present Laughter, alongside Kevin Klein.
"I don't normally like to get very personal on social media but tonight is the opening of this woman's Broadway debut," Killam wrote. "This woman [is] the kindest, most selfless, most stunning individual with the most educated heart I've ever encountered."
The 35-year-old comic actor recalled how Smulders uprooted their lives and came with him to New York City when he got the chance to join the cast of SNL, which is when she "set a goal for herself."
"The only specific creative goal I've ever witnessed her commit to: perform in a play on Broadway," he explained. "In these three years, she has jumped through many hoops; put herself out willingly and vulnerably, while still keeping a priority of being a superb mother and phenomenal partner."
"I have never been so overwhelmed with pride in my life," he concluded his emotional post. "Congratulations, Cobie, you did it. Thank you for the inspiration and the incredible honor of being your husband."
Killam and Smulders tied the knot in 2012 after dating for several years, and the couple share two daughters -- 7-year-old Shaelyn and a 2-year-old daughter whose name they've never revealed publicly.
"We have a family, so the real support comes in being there for each other to study, memorize and train," he shared. "I am unbelievably excited for her and proud. I can't wait to see her on the stage with Kevin Klein -- it's going to be really cool."
Smulders' Broadway comedy, Present Laughter, runs through July 2 at the St. James Theatre.