The proposition initially raised a few hackles - with both church officials and gay activists insisting the other postpone their event - but ultimately went off without a hitch at the city's famed Copacabana beach.
The celebrations began with hundreds of the faithful marching through the streets to honor Our Lady of Aparecida, the country's patron saint.
By midmorning, participants in the World Half Marathon Championship zipped along the beachfront, while at noontime parents took their young ones to Children's Day events by the sea.
As evening arrived, the raucous gay pride parade had taken control, with go-go boys gyrating in time to electronic dance music atop 20 semi-trucks.
Few seemed to mind the confluence of such different events. "I think there is space for everyone," Sandra Cannone, who participated in the religious procession, told the O Globo newspaper.
Guilherme Cruz, 20, attending the gay pride parade, said he didn't mind sharing Copacabana's space.
"I don't have any problems with the church procession," he said. "But we have to fight for our rights as homosexuals. We also have the right to be here."