Little is known about Reeves' early life. Even his birthdate is contested; although he may have graduated from Warren Western Reserve High School in Warren, Ohio in 1968, drummer Dallas Taylor recalled that Reeves had a fake driver's license (procured by Rick James) showing his age to be 19 and was rumored to be as young as 15 in 1969. Reeves has partially corroborated Taylor's account, noting that he was "very young" during his tenure with CSNY.
It has been reported that Reeves was employed as a session bass player with Motown Records when he was 12; although he was scouted at that age by Motown and Chess Records, his mother "would not hear of" him forsaking his education to work as a professional musician at that juncture. Despite having been credited with playing bass on The Temptations' "Cloud Nine", Reeves claimed in a 2012 interview that he was apprehensive during the recording session and switched to tambourine at the behest of producer Norman Whitfield, his recruiter and main benefactor at Motown. During this period, he was also mentored by other Motown luminaries, including the aforementioned James (who concurrently played alongside Reeves in Salt 'N' Pepa, a Los Angeles rock group formed from the remnants of Merryweather) and James Jamerson. He has since contended that his most notable performance for the company was the bass part (overdubbed in Los Angeles) of "No Matter What Sign You Are," the final song recorded by Diana Ross with The Supremes.
Reeves recorded and toured with Crosby, Stills, Nash & Young from August 1969 to January 1970 and is credited on the cover of their 1970 Déjà Vu album; he appears with the group in the concert documentary Celebration at Big Sur (filmed in September 1969) and in contemporaneous television appearances on This is Tom Jones and The Music Scene.
While it was previously assumed that James referred the bassist to Young (who had previously backed James in The Mynah Birds) in the wake of the band's rehearsals with former Buffalo Springfield bassist Bruce Palmer, according to Reeves, "David [Crosby] and Graham [Nash] drove up to the apartment where we lived on Olive Drive at the time... from the pool I saw them knock on the door, and Rick yelled for me. They asked Rick James who I was and Rick came, got me and brought me out front to the limousine that Graham Nash and David Crosby were in and asked me in front of them, would I mind going with them to jam. I asked Rick James 'Aren’t you coming, too?' He said 'They want you to come alone.' I went back to the house, grabbed my Fender Precision Bass guitar and Gibson acoustic guitar, climbed into the limousine and never came back to Rick’s house again. They would not let me go. From the first time jamming with me, they would not let me leave... to this day I don't how Graham and David knew where Rick and I lived."
In consultation with other band members, Stephen Stills fired Reeves from the group in April 1970 "because [he] suddenly decided he was an Apache witch doctor." Stills further opined that Reeves "freaked too much on the bass and no one could keep up because [he] did not play one rhythm the same… he could play bass imaginatively, but he has to be predictable as well," while Reeves also wanted to sing some of his songs during CSN&Y shows, which Stills thought "was ludicrous, only because the songs weren't great. We'll sing any song if it's great, but not just because it happens to be written by our bass player." Dallas Taylor (who seldom fraternized with Reeves and was dismissed from the group a month later at the instigation of Neil Young) later noted that while the bassist and Stills did not get along, Reeves and Young were good friends. Following Reeves' termination, Young defied his bandmates and continued to collaborate with Reeves. Reeves has alleged that the "bass hook" of one of his songs was appropriated by Stills for the main riff of "Carry On"; heeding the advice of James, he demurred from pursuing the issue after receiving a profit point on Déjà Vu. Although he has conceded that "[the band] thought I was trying to put spells on them" due to his trenchant interest in Native American shamanism, Reeves ultimately ascribed his termination to "Stills [having] a problem with himself, just dealing with himself."
Few details are known about Reeves' life and career following his dismissal from CSNY. He reportedly earned an associate's degree in Mandarin Chinese at Coastline Community College during the intervening decades, while his song "I Got Your Number" has been covered by such artists as Tom Jones, Boz Scaggs, and Johnny Bristol. Other unreleased songs allegedly recorded for David Geffen and Clive Davis (including "Working Man") have been championed by Graham Nash and Neil Young; an unreleased cache of his recordings from the early 1970s features a band including Stevie Wonder on drums and Nils Lofgren and Duane Allman on guitar. His 1978 $1 million lawsuit pertaining to unpaid CSN&Y royalties was eventually settled amicably. In the aftermath of his tenure with the group, Reeves nevertheless contributed in earnest to several projects, including most of Neil Young's After the Gold Rush, Crosby & Nash's eponymous debut ("Immigration Man"; 1972), Dave Mason's It's Like You Never Left (1973), an unreleased version of "Tonight's the Night" recorded by Young in early 1974, and indeterminate recordings with George Clinton following the temporary dissolution of Parliament Funkadelic in the early 1980s. Lofgren claimed that during one of the sessions for After the Gold Rush, Reeves appeared covered head to toe in gold paint; Young explained the bassist was "doin' his Indian thing."
Reeves was briefly interviewed by author Jimmy McDonough for Shakey, his 2003 biography of Neil Young. Both Young and Lofgren continue to laud Reeves' playing style, noting his versatility and ability to move fluidly between simple and complex bass lines. Dallas Taylor told an interviewer in 2007 that he had not spoken to Reeves since he was fired from CSN&Y in 1970. Reeves was rumored to have spent time in jail; according to Reeves, from September 1977 to April 1978 "I spent time in a Mexican jail with the Mexican president’s nephew as a political prisoner, because we had tried to smuggle marijuana across the border. True story! Neil Young sent me money (via Western Union) to pay the Mexican police (Judicial Government Police) for my freedom."