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Early days 
He learned accordion from Martin Donaghue. He saw Matt Molloy and James Galway on television and suddenly decided to take up the Irish flute. Seamus won the all-Ireland championship on four different instruments by the time he was 14.
Later work 
When Mick Moloney founded Green Fields of America in 1977, Seamus joined up and took lessons from Mick on the banjo. Two years later he returned to Ireland and won the All-Ireland championship on banjo and mandolin. In 1985 he recorded a solo album Traditional Music Of Ireland.
In 1992 he joined Susan McKeown's band The Chanting House and appeared on a live album with them. Eileen Ivers was also a member of the band. In 1994 he founded Solas and has been on every one of their albums. In 1995 he recorded music for the quirky low-budget film The Brothers McMullen, directed by Edward Burns. He also co-wrote the hit "I Will Remember You" with Sarah McLachlan.
Egan is also the producer for Solas and has worked as producer for other artists, including American singer-songwriter Antje Duvekot.
He has a younger sister named Rory who is a very good concertina player. She graduated from St. Francis Xavier University in Antigonish, Nova Scotia, Canada. He has another sister named Siobhan who was the chief fiddle player in Cherish the Ladies for many years.
Solo albums 
- Traditional Music Of Ireland (1985)
- A Week In January (1990)
- The Brothers McMullen (Soundtrack) (1995)
- When Juniper Sleeps (1996)
- Celtic Tapestry (1999)
Seamus Egan, Eugene O'Donnell & Mick Moloney 
- Three Way Street (1993)
As Session musician 
- Eileen Ivers, "Wild Blue" (1996)
With Solas 
- Solas (1996)
- Summer Spells and Scattered Showers (1997)
- The Words That Remain (1998)
- The Hour Before Dawn (2000)
- The Edge of Silence (2002)
- Another Day (2003)
- Waiting for an Echo (2005)
- Reunion-A Decade of Solas (CD/DVD) (2006)
- For Love and Laughter (2008)
- The Turning Tide (2010)