In the nearly seven years since Eric Garner died at the hands of the police in Staten Island, his mother, Gwen Carr, has helped turn her son’s cries of “I can’t breathe” into a national movement against discriminatory policing.

Ms. Carr has also become a sought-after endorser for political hopefuls looking to represent themselves as candidates of change, especially on policing matters.

That is especially true in New York City’s crowded Democratic primary for mayor, where several candidates have been coveting Ms. Carr’s endorsement in the wake of the national protests that followed the death of George Floyd in Minneapolis last year.

But instead of giving her endorsement to one of the more liberal, progressive Democratic candidates, Ms. Carr will announce on Thursday that she will endorse Raymond J. McGuire, a former Wall Street executive who served on the New York City Police Foundation and who has embraced calls to reform the police, but not defund them.

Mr. McGuire, formerly the vice chairman at Citigroup, is a moderate Democrat who was recruited to run by the city’s business community and quickly raised $5 million in three months. But he still must overcome his lack of name recognition among most voters, and expand his appeal beyond the Wall Street elite.

Ms. Carr’s endorsement could help Mr. McGuire with some left-leaning voters and shore up support in the Black community, which makes up 26 percent of the electorate.

“Eric Garner and George Floyd are examples of what can happen to any Black man in this country and what has happened to all too many Black men in this city,” Mr. McGuire said in an interview. “Gwen Carr’s endorsement means she recognizes that I have what it takes to lead this city and to reflect the voice of those who would not otherwise have a voice.”

Ms. Carr said the next mayor can only undertake the necessary police accountability reforms if the city’s future and finances are stabilized.

“We know that the budget is in a mess, and from what I read he can balance budgets,” Ms. Carr said. “I have grandsons and granddaughters growing up in this city and I want it to be a safer place for them.”

Mr. McGuire, who is Black, has adopted a policing stance that echoes that of Black lawmakers in the city who resisted calls to defund the police last year, citing rising violence in the communities they represent.

“Black people want better policing. We want to reform, restructure and reallocate the dollars,” Mr. McGuire said. “We want our policing to be respectful, accountable and proportionate.”

Mr. Garner was killed in 2014 after being placed in a chokehold by a police officer, Daniel Pantaleo. A grand jury did not indict Mr. Pantaleo and federal prosecutors decided against pursuing civil rights charges. Mr. Pantaleo remained on the police force for five more years until he was fired and stripped of his pension in 2019 by the police commissioner at the time, James P. O’Neill, after a police administrative judge found him guilty of violating a departmental ban on chokeholds.

Ms. Carr said that her pursuit for justice in her son’s death was caught up in politics. She has been critical of Mayor Bill de Blasio’s decision to delay a departmental trial and not fire Mr. Pantaleo. The mayor was elected in 2013 on a promise to overhaul the relationship between the New York Police Department and Black, brown and poor communities.

“He has never been a politician,” Ms. Carr said of Mr. McGuire. “We need new blood.”

Ms. Carr said she admired Mr. McGuire’s support of the National Action Network, the civil rights organization headed by the Rev. Al Sharpton. The group has been one of her biggest supporters since her son’s death. Mr. Sharpton has credited Mr. McGuire as one of many anonymous Black businessmen who had helped fund his organization during difficult times.

Mr. McGuire’s campaign will reveal the endorsement on Thursday in a digital ad created by John Del Cecato, who is responsible for the successful 2013 campaign ad that featured Mr. de Blasio’s son, Dante; and Mark Skidmore, chief executive of Assemble the Agency, who wrote the script for Mr. McGuire’s campaign launch video that was narrated by Spike Lee.

In the nearly two-minute ad, Mr. McGuire and Ms. Carr visit the location in Staten Island where Mr. Garner had his fatal interaction with the police. Ms. Carr holds onto Mr. McGuire’s arm as they walk toward the location, which is commemorated with a plaque and a mural. He refers to her as “Mother Carr”; she calls him “Mr. McGuire,” but he tells her to call him Ray.

Her endorsement will be a disappointment to other candidates such as Eric Adams, the Brooklyn borough president, and Maya Wiley, a civil rights lawyer who was Mr. de Blasio’s legal counsel and former head of the Civilian Complaint Review Board, said Susan Kang, an associate professor of political science at John Jay College of Criminal Justice.

“There are some moderates in the reform criminal justice world for whom this will carry a great deal of legitimacy, particularly those of Ray McGuire’s and Gwen Carr’s generation who are very likely voters,” Professor Kang said. “Trust is an important issue among older voters and that group makes up a high percentage of people who turn out to vote in municipal primaries.”