The 53-year-old actor picked up the accolade for his performances in both "The Master Builder" and "Richard III" at a star-studded bash held at London's Old Vic Theatre, reported BBC.
The veteran actor beat off stiff competition from Sir Ian McKellen, Kenneth Branagh, James McArdle and O-T Fagbenle to take home the Best Actor statuette.
Best Play went to "Harry Potter and the Cursed Child" and was presented to director John Tiffany by Dame Maggie Smith.
Speaking on stage, he said: "It's a show about the peril of isolation, about unity, about family and about love."
More From This Section
Prince William presented David Attenborough with the Beyond Theatre award for his outstanding contribution to broadcasting.
John Malkovich was given the Milton Shulman Award for Best Director for "Good Canary" and Kenneth Branagh was given the Lebedev Award for his performances at London's The Garrick theatre.
"Sunset Boulevard" star Glenn Close was awarded the Best Musical Performance prize from Elton John, who co-hosted the ceremony with the Evening Standard's owner Evgeny Lebedev.
Other stars in attendance included Mark Rylance, Orlando Bloom, Joan Collins and James McAvoy.