Day-Lewis won the prize for outstanding performance by a male actor in a leading role in a theatrical motion picture for his portrayal of a self-made oil tycoon in "There Will Be Blood."
"I'm very, very proud of this. Thank you so much for giving it to me," he said, upon accepting his SAG statuette. "I'm very proud to be included in that group of wonderful actors (nominated for SAG awards) this year."
Day-Lewis then dedicated his award to Heath Ledger, the "Brokeback Mountain" and "I'm Not There" actor who died unexpectedly last week at the age of 28.
Christie earned the SAG award for outstanding performance by a female actor in a leading role in a theatrical movie for her work in "Away from Her," while Bardem won the supporting actor prize for his performance in "No Country for Old Men" and Ruby Dee won the supporting actress accolade for her role in "American Gangster."
The cast of "No Country for Old Men" also won the SAG award for outstanding performance by an ensemble in a theatrical motion picture.