The 23-year-old made 14 appearances for the Latics during an injury-hit 2025-26 campaign and becomes Wigan's eighth signing of the summer as Gary Caldwell continues to shape his squad ahead of the new season.
Trevitt, who made one Premier League appearance during his time at Brentford, is reuniting with Caldwell for the third time, having previously been taken on loan by the head coach twice during spells at Exeter City.
That familiarity played a significant part in the move. "I love playing for Gary. I know exactly what he wants from me on the pitch and off the pitch," Trevitt told the club website.
"Gary gives you freedom to express yourself and show what you can do, whilst also being in a good structure. In the times I've played under him, I've done well, so hopefully I can continue that.
"I see this as a fresh start. There's nothing better than playing football every day, and having games week to week, so I cannot wait to get back into that rhythm."
Trevitt's career has been repeatedly disrupted by injuries, with both of his loan spells at Exeter cut short by fitness issues, while a thigh problem and subsequent hernia surgery also hampered his time at Wigan last season.
Making the move permanent gives him a fresh platform to build some consistency after a stop-start few years, and having already worked under Caldwell on two previous occasions, he arrives at the DW Stadium with a clear idea of what is expected of him both on and off the pitch.
Trevitt came through the ranks at non-league Leatherhead before being picked up by Brentford, and he has represented the Bees' B team in cup success at both London Senior Cup and Premier League Cup level. His permanent departure brings the curtain down on a five-year association with the west London club, during which he made only a handful of senior appearances but earned a reputation as a talented and popular figure within the academy set-up.
For Wigan, tying him down on a permanent basis represents a low-risk addition given his existing familiarity with Caldwell's methods and his performances whenever fit last season.