Sean Mackin is an American rock musician. He is best known as the violinist and backing vocalist for the American rock band Yellowcard and the only original member left in the band.

Yellowcard is an American rock band that formed in Jacksonville, Florida, in 1997. The lineup currently consists of lead singer Ryan Key, lead guitarist Ryan Mendez, bassist Josh Portman and violinist Sean Mackin. Primarily a pop-punk group, their music is recognized for having a distinct sound in its genre, primarily due to the prominent use of a violin in their songs, and are best known for their singles "Ocean Avenue", "Only One", and "Lights and Sounds". Released in 2003, "Ocean Avenue" and its parent album of the same name are both certified double platinum in the US by the Recording Industry Association of America (RIAA); "Only One" and the band's 2006 album Lights and Sounds have been certified gold. The band has released ten studio albums, with its most recent, Yellowcard, released on September 30, 2016. Following this release and supporting tour, the band broke up. The band reunited in September 2022 for a performance at Riot Fest and embarked on a 20th-anniversary tour for Ocean Avenue in 2023. A new EP, Childhood Eyes, was released on July 21, 2023.