Although fairly inauspicious upon initial release, "Relax" finally reached number one on the UK singles chart on 24 January 1984, ultimately becoming one of the most controversial and most commercially successful records of the entire decade. The single eventually sold a reported 2 million copies in the UK alone, making it the seventh best-selling single in UK singles charthistory. Following the release of the group's second single, "Two Tribes", "Relax" rallied from a declining UK chart position during June 1984 to climb back up the UK charts and re-attain number-two spot behind "Two Tribes" at number one, representing simultaneous chart success by a single act unprecedented since the early 1960s.
Upon release in the United States in late 1984, "Relax" repeated its slow UK progress, reaching number 67 upon initial release, but eventually reaching number 10 in March 1985.
The song won Best British Single at the 1985 Brit Awards.
The song was used in the films Body Double, Police Academy, Gotcha!, Bony a klid, Zoolander and The Proposal. It was featured in an episode of Miami Vice, and in the video game Grand Theft Auto: Vice City Stories, Saints Row: The Third, and a 2009 television advertisement for Virgin Atlantic, marking 25 years since the company's foundation.