John Wells had wanted to create a show about paramedics for some time due to his work on ER, but initially felt he didn't have enough material to sustain such a series.

Co-creator Ed Bernero, a former Chicago police officer, wanted to make a police drama partly based on his own experiences; he and Wells had previously worked together on the short-lived show Trinity before teaming up for Third Watch.

The show originally was only going to focus on police officers and paramedics, with the firefighter element added later after producers decided they needed a fire department presence.

Eddie Cibrian originally auditioned for the role of Bosco but lost the part to Jason Wiles; because producers were impressed by Cibrian's looks and the attention he drew, they created the new firefighter character Jimmy Doherty for him instead.

While appearing on Third Watch, Eddie Cibrian was simultaneously playing the contract role of Cole on the soap opera Sunset Beach until that show was cancelled in September 1999.

Eddie Cibrian's 2004 departure from the show marked the first time a main character was written out of Third Watch without dying.

Molly Price's character Faith Yokas made very few appearances in season five because Price was pregnant for much of the season; writers explained the absence as the character recovering from a shootout injury, and her growing belly was often hidden by blankets in the scenes she did appear in.

The season three episode 'In Their Own Words,' which featured interviews with real NYPD and FDNY members who responded to the September 11 attacks, won a Peabody Award.

Molly Price appeared in an interview segment of 'In Their Own Words' because she is married in real life to FDNY firefighter Derek Kelly, who also made recurring guest appearances on the show.

The show's theme song was 'Keep Hope Alive' by The Crystal Method, except in the pilot episode, which used 'Right Here, Right Now' by Fatboy Slim during its opening sequence.