Herron was born on 14 December 1948 in Lisburn, County Antrim to Francis Scott and Elizabeth Herron. He grew up in Leitrim, County Down, a small village near Castlewellan. From an early age he was drawn to motorcycling through the influence of his uncles James and Wilfie, moving from grasstracking around the village into road racing and short-circuit competition. He purchased one of his first motorcycles from his uncles in 1968, modified it for racing, and entered his first road race at the age of 19 at the 1968 Tandragee 100 on a 250cc Greeves.
Herron began competing in earnest in 1965, accumulating experience through numerous events across Ireland. His first significant result came in 1970 when he won the 350cc class at the North West 200. He continued to develop his craft throughout the early 1970s on the demanding street circuits where overtaking opportunities were scarce and local knowledge was everything.
After winning the Irish 350cc championship in 1973, Herron stepped up to the Grand Prix world championships. Racing as a privateer against teams with full factory support, he took on what was described as a David versus Goliath contest. Despite the resource disadvantage, he consistently delivered results that belied his independent status.
During this period he met Andrea, sister of Norton rider Peter Williams, whom he later married. The couple had twin daughters, Kim and Zoë.
At the close of the 1976 season Herron finished fourth in both the 250cc and 350cc world championships. That same year he won the Senior TT at the Isle of Man TT, claiming the final Senior TT to carry FIM world championship status before the event was stripped of that designation. In 1977 he finished runner-up in the 350cc world championship, behind Yamaha factory rider Takazumi Katayama. In 1978 he continued his strong form as a privateer, recording fifth and sixth places in the 250cc and 350cc world championships respectively.
For 1979 Herron finally secured full works, manufacturer-backed support, joining the Texaco Heron Suzuki team in the 500cc world championship. His teammates were two-time 500cc world champion Barry Sheene and Steve Parrish. The season opened promisingly: a third place in Venezuela, a third in Italy, and a fourth in Austria left him third in the championship standings after three rounds.
At the fourth round in Spain he crashed in practice, breaking his right thumb and suffering third-degree burns, which prevented him from racing. He ultimately finished the season in tenth place in the championship.
After the Spanish round Herron returned to Northern Ireland to contest the 1979 North West 200, a race he had dominated in 1978 when he won two events and set a lap record of 127.63 mph — a course record that still stands owing to subsequent alterations to the circuit.
The 1979 North West 200 became known as "Black Saturday." The event claimed the lives of Scottish rider Brian Hamilton, Frank Kennedy of Armoy (who died of his injuries months later), and Herron himself. During the final lap of the last race, Herron was fighting for third place alongside Jeff Sayle, Steve Parrish, and Greg Johnstone when he crashed at Juniper. He was taken to Coleraine hospital, where he died later that day.
Tom Herron was buried at Leitrim Presbyterian Church, near the village where he had grown up.
Herron's career stands as a testament to what a determined privateer could achieve against factory opposition in the competitive Grand Prix motorcycle racing landscape of the 1970s. His fourth and runner-up championship finishes in 250cc and 350cc classes came without manufacturer backing, making them all the more remarkable. His victory in the 1976 Senior TT, later recognised as the last Senior TT held as a world championship round, remains a significant moment in the history of the Isle of Man races.
The North West 200 circuit's standing lap record, set by Herron in 1978 and never beaten due to course alterations, serves as a lasting marker of his speed on the streets of County Antrim. He died at 30 years of age, at the very point when factory support had finally arrived and when a challenge for the 500cc world championship had become a genuine prospect.