A lawyer has pleaded guilty to manslaughter after a 2015 drunken driving crash that fatally injured a 21-year-old motorist on the Long Island Expressway, court records show.

Raj Jadeja, 36, of Brooklyn, also pleaded guilty Thursday in Nassau County Court to charges of assault and driving under the influence of alcohol and drugs, according to the records.

The Sept. 19, 2015 crash in Plainview killed George Ragotte, a Ronkonkoma resident. The young car mechanic had been driving home from his girlfriend’s house in Levittown when, authorities said, he slowed to avoid a different crash and Jadeja’s 2012 BMW sedan rear-ended his car.

It happened on the LIE’s eastbound side at about 2:13 a.m., trapping Ragotte in the wreckage of his 1992 BMW sedan before he died hours later at Nassau University Medical Center, authorities said at the time.

Jadeja’s actions also injured a driver who had been standing outside his vehicle after that motorist was involved in the first wreck, according to police. They said that before the fatal impact, Ragotte had slowed his car to avoid two disabled vehicles that had sideswiped each other east of Sunnyside Boulevard.

Jadeja got a judge’s commitment for an upcoming prison sentence of 1 to 3 years for manslaughter and 2 years for assault under the terms of his negotiated plea with the prosecution, authorities said Friday.

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He will serve the prison time, which also will include 1-year terms for two misdemeanor DWI convictions, at the same time, officials said.

Ragotte’s family has said he graduated from Sachem North High School in 2012, and was a “kindhearted young man” who raced BMX bicycles and dreamed of becoming a pro race car driver.

The defense has said in the past that the fatal crash was caused “by the reckless conduct of other drivers,” and not the actions of Jadeja, a Hofstra law school graduate. His attorney couldn’t be immediately reached for an interview Friday.

Jadeja remains free on $275,000 cash bail, according to court records, which list his sentencing date as May 25.

Nassau district attorney’s office spokesman Brendan Brosh said in a statement Friday that Jadeja “took the life and future of a 21-year-old man” when he struck the victim’s car while speeding, drunk and high.

By his plea, Jadeja has “taken responsibility for the death,” Brosh added.