The 34-year-old attacking midfielder was linked to several clubs around the world after leaving Atletico Mineiro in July.
But the former Paris Saint-Germain, Barcelona and Milan star is heading to Mexico.
Queretaro confirmed the signing in a statement on their website, while Ronaldinho tweeted he would be wearing the number 49 shirt.
The club said they were "very pleased" to bring Ronaldinho to Liga MX, in which they sit seventh through seven games.
Ronaldinho, a 2002 World Cup winner, has won multiple team trophies, is a two-time FIFA World Player of the Year and a Ballon d'Or winner.
He was in-demand after leaving Mineiro, linked to clubs in the United States, Australia and several others in Europe.
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