Since 2010 he has co-written and co-produced hits like "What Makes You Beautiful", "One Thing", "Live While We're Young", "Kiss You" by One Direction and "Starships" and "Pound The Alarm" by Nicki Minaj. In 2012 Carl was listed as No. 4 on Music Week Top 100 Songwriters of the year based on the UK's 100 biggest – selling singles of the year. The same year "Starships" also made US Billboard history, by both debuting in and spending a total of 21 consecutive weeks in the US Top Ten, passing the Black Eyed Peas's single "I Got A Feeling". As of February 2013, it has sold 7.2 million digital downloads world wide. Subsequently, he received two ASCAP awards for most performed songs of 2012: "Starships" and "What Makes You Beautiful".
His favourite instrument is the guitar as he tries to "always have guitar on my songs, almost like a trademark". Carl can also play multiple other instruments like bass, piano, violin and drums, which he started to learn from an early age on during his childhood.