The instrumental lineup became official band members to the Isleys in 1973 resulting in platinum success with the band's rock-infused 3+3 album. For the next ten years, Marvin laid down the bass work for some of the band's funkiest jams and sentimental ballads including Fight the Power, I Wanna Be With You, The Pride, Don't Say Goodnight, For the Love of You, Voyage to Atlantis, and Between the Sheets.
The 3+3 lineup splintered into two groups in 1984 with the original Isleys carrying on as the Isley Brothers while Marvin, Ernie and Chris formed Isley-Jasper-Isley. The group released three albums and had a number one hit with the R&B hit, "Caravan of Love".
In 1991, Marvin returned as member of the Isley Brothers with Ronald and Ernie and carried on until 1997 when Marvin developed diabetes. He had both legs removed. He is currently resting and recuperating and living in Atlanta while brothers Ronald and Ernie continued on as the Isley Brothers. Marvin was inducted along with his brothers to the Rock & Roll Hall of Fame in 1992.