Timothy Seth Avett (born 1980) is one of the lead singers and founding members of the folk-rock band The Avett Brothers. Avett sings and plays guitar, drums, and piano for the band based out of Concord, North Carolina. In 2008, their album, The Second Gleam, reached the number ten spot on Billboard.com's Top Independent Albums chart, and stayed there for three weeks.

Seth Avett is the son of Susie and Jim Avett of Concord, North Carolina. He is the youngest of three children. Bonnie, his older sister, was born in 1973, and Scott, his older brother, was born in 1976. Seth was born in Charlotte in 1980. His father owns a welding business in Concord, and his mother teaches school. Seth's wife's name is Susan.

Seth and Scott Avett were heavily involved with their respective bands during their college years. During this time, Scott was playing with Nemo in Greenville and Seth was involved with the Charlotte-based band Margo, which was started by high school friends. Seth Avett was lead singer and played lead guitar, Noah Warner was drummer/guitarist/singer/writer, Kenny Graham was back-up guitarist, and Ben Sawyer was bass guitarist. Seth and Noah grew up best friends from about the 5th grade, they played soccer together and started playing music together. While in high school they started their first band, "Nothing". They eventually changed to the Margo moniker putting on shows at the local Lions Club and then started playing bars in Charlotte with parents in tow, even winning the local high school Battle of the Bands talent show. Margo had the song "Dumbfight" published on a compilation album with the California production company Rodelle Records. (Scott has been quoted classifying Margo’s music as “melodic rock”.) The brothers decided to merge the bands while maintaining the name “Nemo” in 1998.