Much of the focus on the results of last month’s New York City elections was on Mayor Michael R. Bloomberg’s small victory margin, despite the more than $102 million he spent to secure a third term. But the elections also produced a seismic political shift that so far has gone largely unnoticed: Black, Hispanic and Asian residents made up a majority of voters in a citywide race for the first time.

That turnout is a milestone in a city where minority groups make up both a majority of the population and a majority of those eligible to vote. The transformation of the electorate also signals the growing political importance of the city’s diverse tapestry and the challenges that citywide candidates will face as they strive to stitch together successful voting blocs.

“Legal immigrants are exploding in population and are increasingly registering” once they become citizens “and are now voting,” said Bruce N. Gyory, a political consultant. “All the room for growth in the electorate is amongst Hispanic, Asian, biracial and black New Yorkers.”

The new benchmark has helped minority candidates win prominent offices in larger numbers. Since 2000, William C. Thompson Jr. has been elected the city’s first black comptroller, Helen M. Marshall has been elected the first black borough president of Queens, and John C. Liu, elected last month to succeed Mr. Thompson, has become the first Asian-American to win citywide office. “You’ll see even more diverse candidates in the future,” Mr. Thompson said in an interview last week.