The Doctor Who actor will star alongside Lindsey Duncan, Toby Jones and Douglas Booth in the 90-minute adaptation of Isherwood's famed biography.
He explained that as well as spending time in Berlin in preparation for the part, where Isherwood spent his formative years, he also visited Isherwood's life partner Don Bachardy.
"I went to meet Don who was very charming and inviting, and he said to me that one of Christopher's most memorable qualities was the fact that he was very quiet and very at ease," Smith said of the meeting.
"I think it's very ambitious as a piece of filmmaking. I'm very grateful for them giving me the platform and the opportunity to do it.
"I think that's one of the things about being an actor, you can be anything!"
Christopher and His Kind comes as part of a slew of new dramas produced by the BBC for the Autumn/Winter season.