Mayor Bill de Blasio said on Tuesday that he would not march in the St. Patrick’s Day Parade in Manhattan next month, citing the event’s longstanding tensions with gay and lesbian groups.

Mr. de Blasio will be the first New York mayor in 20 years not to take part in the event, a world-famous procession down Fifth Avenue, which is a highlight of the calendar for many Irish-American groups but also a deeply fraught event for politicians wary of its prohibition on public expressions of gay pride.

“I simply disagree with the organizers of that parade in their exclusion of some individuals in this city,” he said in a news conference at City Hall.

The mayor said he planned to participate in several other events on St. Patrick’s Day, which is March 17, “to honor the Irish heritage of this city and the contributions of Irish-Americans.”