Ainslie began his career as a child actor. He was the producer, director and co-star of the comedic trilogy, Australian Cops (2003). Ainslie moved on to produce more serious films such as "Peace", the recreation of the life events of Alfred Nobel. Ainslie played a small role in the yet to be released film, but is responsible for its screenplay and direction. Since, he has done some acting in commercials for Sony HD Camerasand NBC 4 NY and has worked with Bruce Willis, Ned Vaughn, Radha Mitchell, Rosamund Pike, Devin Ratray, Ving Rhames, Brendan Fraser, Brooke Shields, Adam Sandler and Amy Smart in the upcoming sci-fi feature film, The Surrogates, Furry Vengeance, and TV show See Kate Run.
Ainslie has since worked as a journalist, editor, secretary, crew member and Promotions Director on Q30 and has been featured on the MSG TV Network.
Brett has also become well known for his "Brett Ainslieisms"
"There's always a surface to stop the downs in life but for the ups in life there is no limit" "Live your fear. Become your fear. Lose your fear" "The only feeling worse than guilt is regret." "Know your friends. Know your enemies." "Hell is not where sinners go after life. Hell is the state of mind of which believers are in during life."
Ainslie was a highly touted soccer player, wrestler and sprinter. Ainslie carried the Norwell High School Clippers to a state semi final in his senior season (2006) averaging 2 goals a game in the second half of the season and the MIAA state tournament[2] before sustaining a career ending ACL tear.[3]
Following reconstructive surgery Ainslie is still active in the sport of soccer at Quinnipiac University He has also trained for triathlons.
Ainslie was the second of three sons. Both of his brothers have been featured in Ainslie's films both making a debut in the "Battle of Manzikert".