Two gay rights groups will march in Sunday’s St. Patrick’s Day parade in Boston after organizers abolished a longtime ban on lesbian, gay, bisexual and transgender (LGBT) organizations joining the annual Irish-American march.

Boston Pride said this week that parade organizers had accepted its application to participate in this year’s march through South Boston.

“This is a huge step forward in our mission to have inclusivity in our city and in the Boston-area community,” said Malcolm Carey, clerk of Boston Pride’s board of directors, in a phone interview.

The LGBT-rights group will join OutVets, representing gay veterans, in ending two decades of debate over the issue. Organizers had previously held the belief that homosexuality was in conflict with Catholic doctrine, but the ban stood in direct contrast to more liberal sentiments that make up the majority in Massachusetts, which was the first state in the nation to legalize same-sex marriage.

The lifting of the Boston parade’s ban on gay groups came with some controversy. The Massachusetts contingent of Knights of Columbus, an organization of Catholic men, gave up their spot in the parade on Friday, calling the event “politicized and divisive.”

The Conservative Catholic Action League of Massachusetts had been critical of the Knights’ decision to march, accusing them of “an unconscionable betrayal of Catholic moral principles.”

Mayor Marty Walsh, who did not participate in the parade because of its exclusion of gay groups, intends to march on Sunday, which will make him the first mayor to do so in two decades.

Boston’s mayors have skipped the parade since 1995, when the U.S. Supreme Court affirmed the right of the Allied War Veterans Council to ban gay-identified participants.

“With this year’s parade, Boston is putting years of controversy behind us,” said Walsh in a statement.

Joining Mayor Walsh will be the state’s Republican governor, Charles Baker, along with Democratic U.S. Rep. Seth Moulton, a former Marine and Iraq War veteran who plans to march with OutVets. Rep. Moulton calls gay rights “the civil rights fight of our generation.”

Organizers have truncated the parade route by about 50% this year, after the city’s massive snowfall made it difficult to clear roads.