Haste reportedly decided to resign after being informed on Friday that the Department Trial Commissioner found him guilty on all counts and recommended that his employment be terminated.
Ramarley Graham was 18 when he was shot once in the bathroom of his Bronx home in 2012 during a drug investigation.
He was killed in front of his grandmother and 6-year-old brother.
Haste faced departmental charges for demonstrating "poor tactical judgment." He was accused of not taking obvious steps to defuse a fatal standoff that ended in Graham's death.
Upon Haste's resignation, Graham's mother Constance Malcolm released a statement saying in part,
"My son Ramarley was gunned down and murdered by NYPD Officer Richard Haste over 5 years ago. Richard Haste should have been in prison but instead of even firing him, the de Blasio administration let him resign. This is just another example that the de Blasio administration doesn't care about justice and accountability. Every step of the way, the Mayor and NYPD have dragged their heels and have refused to hold officers accountable for murdering my son."
Mayor de Blasio said that the disciplinary trial ended with the right decision - termination.
"Ramarley Graham was a son, a friend and, most importantly, a young man with his whole life left to live. Nothing can take away the profound pain left after his loss, but I hope the conclusion of this difficult process brings some measure of justice to those who loved him," the Mayor said.
Earlier in January, Haste for the first time publicly described the events five years ago that took place in the house when he fired one shot, killing Graham.
"The absolute last thing I ever wanted to do was pull that trigger other than at a paper target," he said.
Haste, department prosecutors claim, should have set up an outside perimeter and called for emergency service officers.
Haste initially faced a criminal manslaughter charge in the death, but the case was dismissed because of a procedural error. A new grand jury declined to indict, and federal prosecutors also declined to bring charges.
The family settled a wrongful death lawsuit against the city for $3.9 million.
Here's an additional report from Candace McCowan:
(The Associated Press contributed to this report.)