The law passed 436-0 on Tuesday, with just one deputy abstaining from voting on the bill, which bans the spreading of "propaganda of non-traditional sexual relations" among minors.
The law in effect makes it illegal to equate straight and gay relationships, as well as the distribution of material on gay rights. It introduces fines for individuals and media groups found guilty of breaking the law, as well as special fines for foreigners.
Minutes after passing the anti-gay legislation, the Duma also approved a new law allowing jail sentences of up to three years for "offending religious feelings", an initiative launched in the wake of the trial against the anti-Kremlin punk band Pussy Riot.
The two laws were widely criticised by Russia's marginalised liberal and human rights communities and come amid a wider crackdown against independent civil activity in the country.
"I have sincere contempt for the Duma's deputies. All, including the so-called opposition. You have now brought fascism to my country," wrote Yelena Kostychenko, a journalist at the independent Novaya Gazeta newspaper.