Lonnie was born into a musical family; his father was a member of Richmond Gospel music group The Harmonizing Four, and Lonnie remembers groups such as the Swan Silvertones and the Soul Stirrers (then featuring a young Sam Cooke) as regular visitors to the house when he was a child. He learned piano, tuba and trumpet in High School and College, graduating from Morgan State University, Baltimore with a Bachelor of Science degree in music education. He has since cited Charlie Parker, John Coltrane and Miles Davis as major influences on his youth. While still a teenager at College, Lonnie became well known locally as a backing vocalist as well as pianist, and played in the Baltimore area with a number of his contemporaries, including Gary Bartz (alto), Grachan Moncur (trombone), and Mickey Bass (bass). He also backed a number of jazz singers such as Betty Carter and Ethel Ennis when, soon after graduating, he began playing live with the house band at the Royal Theater, Baltimore.

Late in 1965 Lonnie joined Art Blakey's sextet, the Jazz Messengers, sharing the piano position with Mike Nock and Keith Jarrett. The Jazz Messengers, together with Miles Davis' group, were one of the main proving grounds for young up-and-coming jazz musicians, experimentally edgy and musically stretching, and both were an ever-revolving door of young modern jazz musicians as modes and moods rapidly changed during a fresh period of experimentation. Beginning with a live session at The Five Spot, New York City, November 9, 1965, Lonnie's time as a Jazz Messenger was fairly short-term, only lasting until a 3-gig engagement at The Village Vanguard 26–28 April 1966;[2] by May 1966 his position was filled by Chick Corea. Unfortunately no recordings exist of this period.

In October 1986 Lonnie moved closer to his musical roots with "Make Someone Happy" (Doctor Jazz, 1986), an acoustic session that included new recordings of several jazz standards by the trio of Lonnie, Cecil McBee and Al Foster, produced by Bob Thiele. However, despite critical acclaim for this work, Lonnie found himself without a recording contract until the turn of the decade, when the small Startrak label released "Love Goddess" (Startrak, 1990) and "Magic Lady" (Startrak, 1991). "I had a lot of idealistic concepts about music, and about the spiritual message I was trying to get across. But most record companies only care about demographics and bottom line sales.". Both of the Startrak albums marked an about turn to the smooth jazz mode of the Cosmic Echoes period, "Love Goddess" featuring vocalist Phyllis Hyman and saxophonist Stanley Turrentine.

Around this time, the emerging hip-hop movement took an interest in Lonnie's earlier work, and he found himself working with rapper Guru, who was mixing hip-hop with jazz in an innovative way. "Guru and the other rappers would tell me how their uncles used to make them listen to me and Miles and Donald Byrd and how they got the message" Smith told Australia's Daily Telegraph Mirror newspaper in 1995. Smith appeared on Guru's groundbreaking "Jazzmatazz, Vol 1" album (Chrysalis, 1993), once again finding a new audience for his earlier work as a result. He had also toured Europe in 1991, but after this short period of activity Lonnie produced little further work in the 1990s. Despite extensive radio play, appearing on a bewildering number of compilation cds and being namechecked and sampled by an increasing number of younger musicians discovering his Cosmic Echoes output, Lonnie spent the next few years mainly involved in setting up his own label, Loveland, and it wasn't until 1998 that Sony International took advantage of his new found audience by reissuing "Exotic Mysteries" and "Loveland" as a double cd. The same year, Lonnie recorded 'Transformation' (Loveland, 1998), once again revisiting the genre he had been most successful in and reuniting with his brother Donald's vocals. For this release he re-recorded "A Chance For Peace (Give Peace a Chance)" (both as vocal and instrumental versions) and "Expansions" as well as "Space Princess".

Since then Lonnie has not recorded, although he has performed live and toured on a number of occasions, especially in Europe and Japan, were he remains popular with new generations of listeners. He has also spent much of his time teaching at various workshops. In 2002, Sony issued a 2-cd retrospective of his Columbia output "Explorations: The Columbia Years", and his compositions remain a feature of jazz fusion orientated radio and cd compilations. The Cosmic Echoes track, "Expansions" has been featured in two videogames: Grand Theft Auto: Vice City and Driver: Parallel Lines, while "A Chance for Peace" featured in Grand Theft Auto 4. He most recently appearing on the Jazz World Stage at the Glastonbury Festival in June 2009.