When Christine C. Quinn became speaker of the New York City Council last January, she inherited a rabble-rousing body that relished its role as heckler of the establishment.

She was the first female speaker and the first to be openly gay, and she had already clashed with Mayor Michael R. Bloomberg over his stand on gay marriage and his plans for a football stadium on the West Side.

But over the last year, Ms. Quinn, 40, has broken with Council tradition and reshaped the institution from a theater of opposition to a rigidly disciplined body where, in exchange for private collaboration, open dissent is barely tolerated.

She has also emerged as an influential partner of the mayor, pushing him to include more lower-cost housing in a tax break program for developers, shepherding his waste plan through a not-in-my-backyard Council, and expanding neighborhood input on West Side rezoning.

High-stakes conflict between the city’s two most powerful officials has suddenly been replaced with a nonideological focus on effectiveness and collaboration.

“Here you have a liberal Irish lesbian woman speaker working well with a Jewish Republican billionaire pragmatist mayor,” said Douglas A. Muzzio, a professor of public affairs at Baruch College. “The political environment has changed.”