Colin graduated from Indiana University in 2005.
He has Irish and French ancestry. He played the guitar and took singing lessons when he was 17. His introduction to the stage was in high-school where he was a part of the choir and was in the background juggling and doing circus tricks, which led him in being part of his first school musical production of Barnum.
As he put it, he "loved it" and the rest is just history.
Donnell has been part of many national stage tours such as Mamma Mia! and Wicked. His first Broadway performance was in Jersey Boys as Hank Mejewski.
Donnell made his television debut by playing Mike Ruskin in the television series Pan American In 2012, Donnell was cast as Tommy Merlyn in television series Arrow, however, he later left the series after the first season"s finale (as his character was killed off), but made a cameo in one episode during the second season and made two different cameos in the third season.
Foreign the summer of 2013, Donnell starred as Berowne in the musical adaption of Shakespeare"s Love"s Labour"s Lost.
He also appeared as Elizabeth Banks" husband in the crime thriller Every Secret Thing, which was released on May 15, 2015. On January 23, 2014, it was announced that Donnell was cast as Monty in the 1960s-era Broadway musical Violet alongside Sutton Foster and Joshua Henry. Which would begin on March 28, 2014 with a special preview, and officially open on April 20, 2014.
On April 28, 2014, it was announced that Donnell joined the cast of concert Bright Lights, Big City, which was performed on June 16, 2014.
On July 18, 2014 it was revealed that Donnell would play Joshua Jackson"s brother in Showtime original drama The Affair. On November 4, 2014, it was announced that Donnell had joined the cast of Broadway Sings P!NK, which would take place on January 19 and 25, 2015.
On November 19, 2014, Donnell joined the cast of City Center Encores" production of the musical Lady, Be Good, alongside Tommy Tune, Erin Mackey and Patti Murin. The show ran for seven performances, from February 4-8, 2015.
The show was passed on.
On May 29, 2015, Donnell joined National Broadcasting Company series, Chicago Medical, as a regular, playing a doctor in trauma surgery.