Casey Affleck won the Bafta for leading actor for his role in Manchester by the Sea.
He said: "The reason I act is because when I was a young kid, my mother would take me to meetings for children of alcoholics. It was therapy but it was acting and acting has been that for me ever since and it's a privilege to get to do this for a living."
He added: "The reason I am here right now tonight is because of Kenneth Lonergan and his sublime screenplay, that really dignifies our everyday lives and struggles with great compassion. I will never be able to express my gratitude to him."
The other nominees were:
- Andrew Garfield
- Jake Gyllenhaal
- Ryan Gosling
- Viggo Mortensen
La La Land won five Baftas at the ceremony on Sunday night, which also saw success for Brits Dev Patel and Tom Holland.
The Hollywood musical about a struggling actress and a jazz musician is expected to pick up a host of awards at this year's Baftas.