He was 59.
A shooting while on patrol in 1986 left McDonald quadriplegic, but he outlasted expert prognosis and dedicated his years to spreading a message of hope and courage to children, cops and violence-worn communities near and far.
"No one could have predicted that Steven would touch so many people, in New York and around the world," NYPD Commissioner James O'Neill said. "Like so many cops, Steven joined the NYPD to make a difference in people's lives. And he accomplished that every day."
McDonald had been on the force for just under two years when he was shot three times and critically injured by a 15-year-old boy on a misty July afternoon in Central Park.
The bullets, striking him in the head, then arm and throat, left him intubated and in a wheelchair.
Doctors said he wouldn't live more than five years. His wife, three months pregnant with their first child, collapsed when she heard the news.
But months later, on the day of their newborn son's baptism, McDonald's wife, Patti Ann, read a letter from her husband that initiated his mission of empathy.
"I'm sometimes angry at the teenage boy who shot me,'' she said, her voice quivering, The New York Times reported then. ''But more often I feel sorry for him. I only hope that he can turn his life into helping and not hurting people. I forgive him and hope that he can find peace and purpose in his life.''
McDonald brought his message to inner-city schools and church groups, and around the world to war-torn communities, including Northern Ireland, Bosnia and Israel.
He campaigned for gun control alongside Michael Bloomberg and against cloning research with George W. Bush.
Propelled by his strong Catholic faith, McDonald was blessed along with his family by Pope John Paul II in 1993.
In 2004, McDonald was promoted to detective first grade with the NYPD. It was with the department, where he'd visit commands and roll calls and preach the importance of teamwork, that McDonald got the most pleasure, O'Neill wrote Tuesday in an internal memo.
New York Mayor Bill de Blasio on Tuesday called McDonald "this city's greatest example of heroism and grace."
"There is no greater example of honor and service to others. Let it be our mission to continue his work," de Blasio said.
McDonald, born in Queens and raised on Long Island, the son of an NYPD officer, the Times said, was also the father to an NYPD officer.
Conor McDonald, 29, joined the NYPD in 2010. Last year, he was promoted to the rank of sergeant.
McDonald is also survived by his wife.
His story, too, lives on.
As recently as November, McDonald spoke with students in New York, CNN affiliate NY1
"Honestly, I thought it was so inspiring how after what happened to him, he's able to forgive the man who did this to him," one young woman told the station.
"To hear his story from his own mouth, to hear that he was so forgiving, it was very moving," another said.