The Scot has been with the Bees for the past four years.
Pressley said: “After careful consideration, I’ve decided it’s time for a new challenge in my career.
“I leave the club having formed some great friendships, great memories, and also being appreciative of the opportunity to work with some highly-skilled people, which has allowed me to learn and grow as a person.”
Director of football Phil Giles added: “I’d like to thank Steven for his commitment to Brentford over the last 4 seasons.
“As well as developing some of our best young players and having a meaningful impact on first-team performances in the Premier League, he’s been a top professional and a pleasure to get to know as a person.
“On behalf of everyone at Brentford, I wish him well in his future career.”