He has played Michael Westen in the television series Burn Notice, and appeared in films such as Hitch, Believe in Me, Changeling, and Come Early Morning.

While attending college, Donovan was a commercial bus driver at UMass Transit Service, where he operated passenger buses as part of the PVTA.

Donovan has guest-starred in several television shows, including CSI: Miami, Spin City, Monk, Millennium, Witchblade, The Pretender, Homicide: Life on the Street and Law & Order.

In 2004, he had his first leading role in the American remake of the British television series Touching Evil with Vera Farmiga on the USA Network.

The show follows Westen as he attempts to find out why he was burned and regain his job as a covert intelligence agent, in addition to bringing justice to the people of Miami.

Donovan also directed a prequel film starring co-star Bruce Campbell, titled Burn Notice: The Fall of Sam Axe, which first aired on USA Network on April 17, 2011.

[11] Donovan has also performed on stage in various productions, including Hamlet as the title character, A View from the Bridge as Marco, An Inspector Calls, and Off-Broadway in Things You Shouldn't Say Past Midnight as Gene, The Glory of Living as Clint, regionally in Toys in the Attic as Julian Berniers, On the Waterfront as Terry Malloy, Oedipus as Teiresias and Freedomland (play) as Seth.

[18] For many years, Donovan has actively supported Life Rolls On (LRO), a foundation empowering people with spinal cord injuries.

In September 2009, while helping Michael Bolton at the 17th Annual Benefit Concert for Women and Children at Risk in Stamford, Connecticut, Donovan auctioned off a "Burn Notice walk-on-part" plus a kiss.