Lemma seized control in the opening miles and built a lead of more than two minutes by the halfway mark on the way to victory in 2:06:17.
By the time those chasing could make any inroads on his lead it was too late and Lemma finished 41sec ahead of compatriot Mohamed Esa - who surged late to grab second ahead of Kenyan Evans Chebet, who was denied a third straight Boston title.
Lemma's gritty wire-to-wire victory was a marked contrast to the late push Kenyan Hellen Obiri (34) delivered to win her second straight women's title in 2:22.37.
In a race that saw 19 women clustered in a leading group at the halfway point, Obiri and compatriots Sharon Lokedi and Edna Kiplagat finally separated themselves in the final three miles.
Obiri and Lokedi ran shoulder-to-shoulder before Obiri pulled away in the final mile, Lokedi finishing eight seconds back and Kiplagat completing the Kenyan podium sweep 44 seconds adrift.
Lemma, whose personal best of 2:01:48 makes him the fourth-fastest marathoner in history, was on pace to shatter the Boston course record of 2:03:02, set in 2011 by Kenyan Geoffrey Mutai.
He finished with the 10th-fastest Boston time ever, the draining hills on the second half of the course taking their toll and his lead dwindling as Chebet and Kenyan John Korir pushed the pace over the final miles.
Lemma had enough left to preserve his lead as behind him Esa charged past both Chebet and Korir to seize second.
It was Lemma's first marathon victory since his triumph in London in 2021.
It was all the more satisfying on a course where Lemma had twice failed to finish and placed 30th in 2019.
"I was able to redeem myself," Lemma told ESPN. "So I'm happy.
"My plan was to break the course record.
"But it's so hilly, up and down, and that took a lot and made me tired."
Lemma said the challenges posed by the course were perfect preparation for the 2024 Paris Olympics marathon.
"The reason I came to run in Boston was because Boston Marathon is similar to the Paris Marathon - up and down the hills. It will help me there."
