Timmons was born in Philadelphia, Pennsylvania, the son of a minister. He had a sister, Eleanor. Both of his parents, and several aunts and uncles, played the piano. From an early age Timmons studied music with an uncle, Robert Habershaw, who also taught McCoy Tyner.

Timmons left Blakey for the second time in June 1961, encouraged by the success of his compositions, including jukebox plays of "Dat Dere", which Oscar Brown had recorded after adding lyrics. Timmons then formed his own bands, initially with Ron Carter on bass and Tootie Heath on drums. They toured around the US, including the West Coast, but played most in and around New York. In the initial stages of this trio, Timmons liked the group sounds of the trios led by Red Garland and Ahmad Jamal. According to Tootie Heath, Timmons was at the peak of his fame at that point, but was addicted to heroin, and used a lot of the money that the band was paid maintaining his habit.  In 1963 Timmons' playing, with Lewis Powers on bass and Ron McCurdy on drums, was described by a Washington Post reviewer as "flexible and adventuresome [...] Glossing over everything is an undeniable sheen of church music and spirituals." In 1965 the same reviewer commented that Timmons was employing musicians who were of much lower ability: "Timmons lacks a certain passion but I wonder if this is not the fault of his sidemen." Timmons started playing vibes in the mid-1960s. He occasionally played organ, but recorded only one track on that instrument - a 1964 version of "Moanin'" on From the Bottom. Recordings as a leader continued, usually as part of a trio or quartet, but, after joining Milestone Records around 1967, Timmons' album Got to Get It! featured him as part of a nonet, playing arrangements by Tom McIntosh.  Timmons' career declined quickly in the 1960s, in part because of drug abuse and alcoholism and partly as a result of frustration at being typecast as a composer and player of seemingly simple pieces of music. In 1968 he made his second, final, recording for Milestone, Do You Know the Way? In the following year he played in a quartet led by Sonny Red, with Dexter Gordon on one of the saxophonist's temporary returns to the US from Europe, and in a trio backing vocalist Etta Jones. Timmons continued to play in the early 1970s, mostly in small groups or in combination with other pianists, and mainly in the New York area.  According to saxophonist Jimmy Heath, Timmons joined Clark Terry's big band for a tour of Europe in 1974. He was unwell and drank on the plane to Sweden, and fell while drinking at the bar before the band's first concert, in Malmo. Susceptible to blood clotting, he was flown back to the US. On March 1, 1974, he died from cirrhosis, at the age of 38, at St Vincent's Hospital in New York. He had been in hospital for a month. He was buried in Philadelphia, and was survived by his wife, Estelle, and son, also Bobby.

Did he ever have any more success
In the following year he played in a quartet led by Sonny Red, with Dexter Gordon on one of the saxophonist's temporary returns to the US from Europe,