McCartney grew up in Irvington, New York and is the eldest of three children. His parents - trained actors and singers - would put on a musical stage production in the local community theater each year that included the entire family. That experience led McCartney to pursue a career in entertainment. At only 9 years of age, he was cast as Louis, son of Hayley Mills' Anna, in the Broadway production and the national touring company of The King and I. Two years later, McCartney landed the role of the young Scrooge opposite Roger Daltrey in A Christmas Carol at Madison Square Garden.

McCartney's big break came when he was cast in the long-running daytime drama All My Children as Adam Chandler, Jr. He was nominated for Daytime Emmy Awards in both 2001 and 2002 for Best Performance by a Young Actor in a Television Series, as well as for a Soap Opera Digest Award. He won the Young Artist Award for his role in the series in 2001 and 2002. Additional television appearances include a guest-starring role in Law & Order and performances with Sugar Beats and Dream Street on Good Morning America, The Rosie O'Donnell Show and Maury, McCartney has also been featured in many commercials both as an on-screen and voiceover actor.

For over three years, McCartney was a member of the hugely popular teen band Dream Street. Their debut album reached No. 1 on the Billboard Independent Album Charts and soared to platinum sales. Dream Street's songs have been featured on the soundtracks for Pokemon 2000 and The Little Vampire. Prior to Dream Street, McCartney was the lead singer in Sugar Beats, with whom he recorded four albums. McCartney recently released his first solo album, and his first single topped the Radio Disney Top 3 charts for weeks.

McCartney currently lives with his family in New York but will relocate to Los Angeles for the filming of the series. In his free time, he enjoys skiing (on both snow and water) and playing baseball for his high school team. He recently took up surfing for his role in Summerland and has been taking courses in photography. McCartney is planning on going to college and hopes to attend the University of California, Los Angeles, or New York University.