The 27-year-old, who plays Will McKenzie in the E4 comedy, proposed to Lisa Owens during a romantic trip to France.
"Simon took Lisa to Paris without any mention of plans to propose, but he had it all worked out," a source told The Sun. "He bought a ring - sticking to traditions and spending a month's wages on the sparkler.
"They went for dinner and he asked her to marry him. Lisa immediately said, 'Yes'. They are looking forward to spending the rest of their lives together."
The couple met at Cambridge University, when they performed together in a skit written by Bird's Inbetweeners co-star Joe Thomas.
Bird recently described the success of The Inbetweeners as "a double-edged sword".
Watch Digital Spy's recent interview with the Inbetweeners Movie stars Simon Bird, Joe Thomas, James Buckley and Blake Harrison below: