In 1970, a California-based power trio consisting of Tom Johnston, Dave Shogren and John Hartman teamed up with Simmons to form a group together.

"Simmons wrote and sang many songs for the Doobie Brothers, including lead vocal on "South City Midnight Lady", as well as "Dependin' On You", "Echoes of Love", "Wheels of Fortune" and "Black Water", the group's first #1 record.

The Doobie Brothers disbanded in 1982, with Simmons' decision to leave the group, as the last original member at the time, after Dave Shogren left in 1971, Tom Johnston in 1977, and John Hartman in 1979.

[2][3] Upon hearing that the band were to be inducted into the Rock and Roll Hall of Fame, Simmons recalled:[8] I was really happy about it.

With Tom Johnston, Simmons wrote Long Train Runnin': Our Story of The Doobie Brothers (2022).

[15] They participated in the 2016 Motorcycle Cannonball, riding from Atlantic City, New Jersey to San Diego, California.