He is on track to break his personal record of 10 tries in one campaign, having touched down eight times for Ulster so far this season.
Trimble made his Ireland debut against Australia at Lansdowne Road in November 2005. He has won 49 caps and has scored 11 international tries. His last appearance for Ireland was against South Africa in the GUINNESS Series in November last year.
Ulster's director of rugby David Humphreys said: "I am delighted that Andrew has signed a new national contract as he is without doubt a world class finisher and he is a hugely important member of our squad.
"Andrew has now spent almost eight years at Ulster Rugby. This deal will take him to a decade at Ravenhill and that reflects both his remarkable consistency of performance and his unwavering commitment to his province."