[12][13] In January 2014, Donnell was cast as Monty in the 1960s-era Broadway musical Violet alongside Sutton Foster and Joshua Henry; previews began on March 28, and the show officially opened on April 20.

[18][19] In March 2015, Donnell starred in Love Is A Four Letter Word, a pilot for NBC in which he played Sean, an ad agency partner; the show was not picked up to series.

[20] Donnell then landed a regular role in the NBC series, Chicago Med, playing a doctor in trauma surgery.

The production was directed by Kate Whoriskey and starred Shoshana Bean, Colin Donnell, Mykal Kilgore, and Solea Pfeiffer.

[24] In 2024, Donnell was cast in the guest role of Brian Lange in CBS television series FBI: International for the final two episodes of the show's third season.

[25] Donnell began dating actress Patti Murin in 2013 after they co-starred in a Shakespeare in the Park musical adaptation of Love's Labour's Lost.

[31][non-primary source needed] He has two tattoos from his tour trips – one from Memphis and one from Dayton; which are five silhouettes of birds to represent his family, and a Fleur De Lis, because his mother is French.