Dion was pursuing a singing career in his early teens, and made his first TV appearance on a show called Teen Club in 1951. He later recorded "The Chosen Few" with a group called The Timberlanes. In 1957, DiMucci rounded up the best singers he could find and began rehearsing on the subways heading into Manhattan. They called themselves Dion And The Belmonts, after Belmont Street in the Bronx. The group included tenor Fred Milano, tenor Angelo D'Aleo and bass singer Carlo Mastrangelo. By 1958, the group had its first hit with the Doo-Wop sounding "I Wonder Why" (#22) followed by "No One Knows" (#19). The next year, the quartet reached #40 with "Don't Pity Me" before their break-through hit, "A Teenager in Love" (#5). In 1960, the hit parade continued with "Where Or When" (#3), "When You Wish Upon A Star" (#30) and "In The Still Of The Night" (#38).

Dion went solo in 1960 (the Belmonts did some more recordings on their own), moving to more R&B / Pop-oriented tunes with great success. He handled himself with a suave, cocky ease on a long string of hits like "Lonely Teenager" (#12), "Runaround Sue" (#1), "The Wanderer"(#2), "Lovers Who Wander" (#3), "Little Diane" (#8), "Love Came To Me" (#10), "Ruby Baby" (#2), "Donna the Prima Donna" (#6) and "Drip Drop" (#6). These tunes cast him as either the jilted, misunderstood youngster or the macho lover, capable of handling anything that came his way.

By the mid-'60s, his heroin habit (which he'd developed as a teenager) was getting the best of him, and he did little recording and performing for about five years. When he did make it into the studio, he was moving in some surprisingly bluesy directions, which met with little success. In 1968 he kicked heroin and re-emerged as a gentle folk-rocker, and scored a #4 hit single, "Abraham, Martin and John". The song was sort of an anthem for the times, asking why some of America's greatest leaders were killed in their prime. Dion would focus upon mature, contemporary material on his late '60s and early '70s albums, but a follow up hit never appeared. Although his material received positive critical feedback, he managed only moderate sales.

The Folk phase didn't last long. In 1972 he reunited with The Belmonts, and in the mid-'70s cut a disappointing record with Phil Spector as producer. The kinds of music that Dion knew best, Doo-Wop and Folk, were no longer in fashion and he quickly faded from view.

Over the next two decades Dion continued to record and perform to indifferent commercial results, but his critical reputation rose steadily with many noted contemporary musicians showering him with praise and citing his influence. In 1987, he agreed to do a concert of his old hits at Radio City Music Hall in New York. The two disc CD of this concert was released in 2005. Dion was elected to The Rock And Roll Hall Of Fame in 1989 and in 2000, Dion And The Belmonts were inducted in the Vocal Group Hall of Fame. Dion has since issued several albums with contemporary Rock artists. His "Deja Nu" LP in 2000 found him covering Bruce Springsteen, a major supporter over the years. Dion joined the Boss on stage in Miami in 2002 for a performance of "If I Should Fall Behind" from "Dream On Fire".

In January 2006, Dion released "Bronx in Blue", a collection of Blues and Country standards, which was nominated for a Grammy Award. In November of the following year, he issued a follow-up in similar vein, "Son of Skip James". In October 2008, he released "Heroes: Giants of Early Guitar Rock", an album of covers of early Rock 'n' Roll songs that were recorded by Buddy Holly, Ritchie Valens, Ricky Nelson, Johnny Cash and many others. In October 2009, he performed "The Wanderer" with Paul Simon at the 25th Anniversary Rock And Roll Hall of Fame Concert.

A practicing Roman Catholic, Dion pursued a prison ministry and reached out to men going through addiction recovery. He is also a member of the American Board of Directors of Renewal Ministries. He currently maintains homes in Boca Raton, Florida, and New York City. On January 24th, 2012, he released the album, "Tank Full of Blues" to favorable reviews. In November, 2015, Dion announced his latest album, "New York Is My Home" featuring his long-time friend Paul Simon, would be released in January, 2016.

In late April of 2020, amid the COVID-19 virus lock down, Dion announced that a new album called "Blues With Friends" would be released on June 5th. Those friends included Bruce Springsteen, Billy Gibbons, Jeff Beck, Paul Simon, Van Morrison and Brian Setzer. "I needed to round up the best guitarists and musicians alive and pick them from every generation, every variation of Blues," Dion said. Recorded in late 2019 and early 2020, Dion co-wrote all of the fourteen songs included on the album. In mid-November of that year, he released two new holiday songs. The first is a cheery acoustic number called "Hello Christmas", featuring Amy Grant. The second, "You Know It's Christmas", highlights guitarist Joe Bonamassa. Both songs were issued on Bonamassa's label, Keeping the Blues Alive.