“It would make me happy to say yes,” he wrote in a letter to festival director Maria Averbakh. “However, as a gay man, I must decline.”
Wentworth, who was to be honoured at the festival, said he was “deeply troubled” by attitudes in Russia.
The new laws ban the promotion of gay, lesbian or bisexual lifestyles.
In June, the Russian parliament overwhelmingly backed a bill which prescribes heavy fines for anyone organising a gay pride event or providing information about homosexuality to people under 18.
“I am deeply troubled by the current attitude toward and treatment of gay men and women by the Russian government,” wrote Wentworth, 41, in a letter posted on GLAAD’s (Gay and Lesbian Alliance Against Defamation) website.
“The situation is in no way acceptable.”
“I cannot in good conscience participate in a celebratory occasion hosted by a country where people like myself are being systematically denied their basic right to live and love openly.”
Homosexuality was decriminalised in Russia in 1993, but anti-gay sentiment is high.
It has been widely criticised by Western politicians and human rights groups, and gay rights campaigners have launched a tentative campaign for a boycott of the 2014 Winter Olympic Games, due to be held in Sochi in February.
Wentworth, whose mother is of Russian origin, is best known for his role in the award-winning TV series Prison Break, for which he was nominated for a Golden Globe in 2006.
Most recently he wrote the screenplay for Stoker, starring Nicole Kidman and Mia Wasikowska, released in the UK earlier this year.
While his sexual orientation had been the subject of tabloid speculation, the actor had not publicly acknowledged he was gay until the letter was published.