Seiwell was born and raised in Lehighton, Pennsylvania, the son of Donald Seiwell and Fay Carrigan. He has a brother, Darryl. Denny Seiwell is a graduate of Lehighton High School and was a member of the first Carbon County Band in 1961. After graduating from high school, Seiwell enlisted in the United States Navy, in the rate of Musician, playing in the Navy Band. He moved to New York City and caught the eye of Paul McCartney, who recruited him to be in his band Wings and according to Seiwell, the band was like one big family living between London and the McCartneys' farm in Scotland. After leaving the band, Seiwell eventually moved to Los Angeles, where he has resided since 1975.[2][3] Seiwell stated in 2019 that he and McCartney have kept in touch since 1993.[4]
^Slate, Jeff (2019)."In and Out of Wings: Denny Seiwell On His Friendship with Paul McCartney and Wings’ Underrated 1971-1973 Era" Rock Cellar Magazine