Directed by Steven Soderbergh, 'Behind the Candelabra' is a biopic about the last 10 years in the life of pianist Liberace and the secret affair he had with his friend Scott Thorson, played by actor Matt Damon.
Others vying for the lead actor trophy were Matt Damon for 'Behind the Candelabra', Toby Jones for 'The Girl', Benedict Cumberbatch for 'Parade's End' and Al Pacino for 'Phil Spector'.
Amidst the news of marriage trouble, Douglas, 68, walked the red carpet alone, but thanked his wife, actress Catherine Zeta-Jones and his three children - Cameron, Dylan, Carys, on receiving the award.
This is Douglas' first Primetime Emmy Award and fifth nomination.
'Behind the Candelabra' also won the best miniseries/movie award. Steven Soderbergh was honoured with the Emmy's trophy.
The lead actress trophy at the 65th Primetime Emmy Awards was taken by actress Laura Linney for her character Cathy in the miniseries 'The Big C: Hereafter'. This is her fourth Emmy Award, she previously won the award for 'Frasier', 'Wild Iris' and 'John Adams'.
Other nominations in the category were Jessica Lange for 'American Horror Story: Asylum', Elisabeth Moss for 'Top of the Lake', Helen Mirren for 'Phil Spector', and Sigourney Weaver for 'Political Animals'.