Born and raised in Garden Grove, CA, McEuen began learning to play the banjo when he was 18. At that time he was attending college and earning extra money by working at nearby Disneyland; comedian Steve Martin was a co-worker, and McEuen taught him how to play banjo. (Much later, Martin and the NGDB would frequently appear together in concert.) McEuen decided to become a professional musician in 1964 after seeing the Dillards perform live; inspired by their energy and musicianship, he began to study the banjo in earnest. In 1965, he hooked up with Michael Martin Murphey for a year and subsequently performed on all five of Murphey's albums.

In 1966, he was visiting a guitar shop in Long Beach when he met the Illegitimate Jug Band, who had just lost member Jackson Browne and were deciding to regroup. McEuen joined and the group became the Nitty Gritty Dirt Band. He remained with them for over two decades, singing and playing banjo, mandolin, fiddle, and other stringed instruments through the watershed period that produced such classic albums as Uncle Charlie and His Dog Teddy (1970) and the landmark compilation Will the Circle Be Unbroken (1972). McEuen was also there during the band's subsequent dry spells, as they struggled to reshape their style before again finding success in the mid-'80s. For reasons that remain unclear, McEuen abruptly left the Dirt Band in 1987.

During his years with the group, McEuen had played solos at every show and occasionally appeared as a solo act. He also made guest appearances on other albums and did session work for such artists as Bill Wyman, Marshall Tucker, and Hoyt Axton. McEuen also composed music for film and television soundtracks, including the scores for Paint Your Wagon (1969) and Samuel Beckett Is Coming Soon (1993). In 1989, he briefly rejoined the Dirt Band to perform on their Will the Circle Be Unbroken II album. The following year, he directed a concert video and produced an album for the Dillards. In 1992, he released the album String Wizards, an all-star venture featuring such illustrious artists as Earl Scruggs, Vassar Clements, and Byron Berline. A follow-up, String Wizards II, appeared in 1994, at about the same time McEuen founded his own label -- named, appropriately enough, String Wizard. Acoustic Traveller was released in 1996, followed three years later by Round Trip: Live in L.A.. He and former Nitty Gritty Dirt Band member Jimmy Ibbotson came together in March 1999 to record Stories and Songs. The traditional rock-bluegrass sound is combined with behind-the-scenes anecdotes and commentary. Stories and Songs was released in May 1999.