The construction firm employee, who began working on the project in December, clocked 200 hours of overtime in the month.
The construction firm employee, who began working on the project in December, clocked 200 hours of overtime in the month before his body was found in April, attorney Hiroshi Kawahito said in a statement sent to AFP on Friday.
His parents applied for compensation last week and asked the government to recognise his suicide as a case of "karoshi" or death from overwork.
Every year, Japan's notoriously long working hours are blamed for hundreds of deaths due to strokes, heart attacks and suicides.
The news of the suicide comes as authorities hurry to finish work on the showpiece venue for the 2020 Summer Games after initial plans sparked public anger over its $2 billion price tag.
The family's lawyer Kawahito described "extremely tight" working schedules at the stadium site with workers "under heavy pressure".
He said the 23-year-old man, whose name has not been released, went missing in March, leaving a note saying he had "reached the physical and mental limit".
Details on how he committed suicide have not been released.
"We were worried as he had such short sleeping hours," the parents said in a statement released by Kawahito, adding that he would wake up at 4:30 am and come back home after midnight.
"We really don't want other people to die from overwork like our son," they said.
Tokyo's 2020 Olympic organisers said they were "saddened" by the news, adding that would ask operators "to take the utmost care to ensure there is no reoccurrence of such tragic events".
Japan Sport Council, the body overseeing the construction of the stadium, said it was renewing a call to contractors to comply with labour laws.
In December, the head of Japan's biggest advertising agency Dentsu resigned in response to the suicide of a young employee who regularly logged more than 100 hours of overtime a month.
The death of Matsuri Takahashi generated nationwide headlines, prompting the government to come up with a plan asking employers to limit overtime to a maximum of 100 hours per month. But critics say this is still too high.