He died after being attacked on a night out in Omagh in the early hours of New Year's Eve in 2012.
Mark Donnelly, 23, from Greencastle Road, Omagh, denies manslaughter.
The jury was told that Mr Donnelly was convicted of affray, along with four other men, for an earlier street fight involving Mr McGovern and a friend.
The prosecution said this was a prelude to the alleged incident in which Mr McGovern was punched once and fell to the ground hitting his head.
He went back to his friend's house in Emyvale, where he was found dead later that day.
A prosecution lawyer claimed Mr Donnelly may not have intended to kill but was, nevertheless, responsible for causing Mr McGovern's death.
The lawyer said the alleged incident was not captured on CCTV but the jury would hear evidence from two witnesses who saw Mr McGovern being hit by a single punch to the head and falling to the ground.
He suffered a fractured skull and died as a result of bleeding on the brain.
Mr Donnelly told the police that he did not assault Mr McGovern.
The trial at Dungannon Crown Court is expected to last up to three weeks.
The trial has begun of a County Tyrone man accused of the manslaughter of 19-year-old Jason McGovern from Tydavnet in County Monaghan.