Zagar signed with the Toronto Lynx in 1998 and played with them for a total of seven seasons. Where he currently holds every Lynx goalkeeping record: most wins (64), most shutouts (44.5), most saves (665), and most games played (174).
Zagar was named Toronto Lynx Most Valuable Player three times, in the year 2000, 2002, 2003. In 2000 he was named into The A-league Second All-Star Team.
In 2006 when Duncan Wilde returned as Head Coach of the Toronto Lynx, he was appointed to player/assistant coach role, along with team captain Joe Mattacchione. During the season he helped the Lynx to a team-record 10 game undefeated streak at home,and as well helped the Lynx reach the Open Canada Cup final, which they lost 2-0 against Ottawa St. Anthony Italia.
After the 2006 season the Lynx dropped two divisions down into the PDL, Zagar retired shortly after to become the U11 Development Director and Goalkeeper Director for the Oakville Soccer Club in 2007.
Theo's father, Dragan Zagar, is the long-time President and Tournament Chair for the East York Soccer League.
Theo has been recently heard doing the play-by-play for Rogers Television's coverage of the Canadian Soccer League.