The Prison Break star explained that "as a gay man" he did not feel comfortable attending the St Petersburg International Film Festival. Wentworth, 41, was asked to attend as a guest of honour but wrote to the festival director Maria Averbakh turning the offer down.
"As a gay man, I must decline," said Wentworth in his reply. "I am deeply troubled by the current attitude toward and treatment of gay men and women by the Russian government.
"The situation is in no way acceptable, and 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."
Wentworth added that he had enjoyed visits to Russia previously and has a degree of Russian ancestry, and in other circumstances would have been happy to attend.
The actor's letter was made public on the website of GLAAD, a group which works with the media to represent gay, lesbian, bisexual or transgender people and issues, and of which Wentworth is a member.
A spokesperson for the organisation, Wilson Cruz, praised the star's response, saying that it "sends a powerful message to LGBT Russians, who are facing extreme violence and persecution — you are not alone.
"As people from across the globe continue to speak out against Russia's horrific law, more celebrities and corporations should follow his courageous lead in openly condemning Russia's anti-LGBT law," he added.
Some of the homophobic laws introduced by the country's president Vladimir Putin and his government include the banning of public gay pride events, and the banning of the adoption of Russian-born children by gay couples.