Magnús Scheving was born on 10 November 1964 to Þórveig Hjartardóttir and Eyjólfur Magnússon Scheving. His paternal grandfather was Danish. He grew up in the small town of Borgarnes in Iceland. At 15 years old he had his first job as a telephone exchange messenger boy for Borgarnes. In his 20s, he made a bet with a friend, Fjölnir Þorgeirsson, that each could master a sport of the other’s choosing he knew nothing about in three years. Magnús chose snooker for Fjölnir, and Fjölnir chose aerobics for Magnús. Just as Magnús became a champion in aerobics, Fjölnir became Icelandic champion in snooker. He has an older sister and a younger brother.

In 1992, Magnús became the Icelandic Men’s Individual Champion in aerobic gymnastics. In 1993, he became the Scandinavian champion, and was the European champion twice in 1994 and 1995. He was voted Athlete of the Year in Iceland in 1994. In addition to his sports career, Magnús became a well-known and sought after public and motivational speaker around the world. He also from 1991–93 hosted his own chat show in Iceland, with a format where parents could come on and ask him questions about how to raise healthy children. In 1995, he published a children’s book called Áfram Latibær, the first recorded work in the LazyTown franchise. During this time, he was also running a carpentry business, which gave him the money to travel the world. He also was a fitness teacher for teenagers at a local school, having earned a degree in sports science at University of Iceland.

In the 1990s, during a career as an extensive public speaker, Magnús noticed an absence in healthy lifestyle role models for children. It was during this period that he began to compete in aerobic competition both nationally and internationally. In 1995, he published Áfram Latibær, a children’s book which explains the importance of a healthy lifestyle. The book was adapted into a stage play of the same name directed by Baltasar Kormákur. The show toured Iceland from 1996–1997 and made LazyTown a household name across the country. It was shown to be immensely popular among children and so, a sequel was written, Glanni Glæpur Í Latabæ, which was the first time Robbie Rotten was introduced, played by Stefán Karl Stefánsson.

LazyTown was commissioned by Nickelodeon in May 2003 and the first episode aired on Nick Jr. on August 16, 2004.

Magnús is the CEO, creator, and co-founder of LazyTown Entertainment. This company produces books, videos, games, and sporting goods to help promote fitness and a healthy lifestyle to children. He is also creator of the show LazyTown (Latibær in Iceland), where he played Sportacus (known as Íþróttaálfurinn in Icelandic) from 1996–2014. In 2006, Magnús received a Lifetime Achievement Award at the Icelandic Edda Award ceremonies for his work as founder and creator of the LazyTown franchise. Ólafur Ragnar Grímsson, President of Iceland, presented the award to him. Magnús starred in the 2010 film The Spy Next Door in which he portrayed a Russian villain attempting to destroy all of the world’s oil supplies.

After LazyTown Entertainment was bought by Turner Broadcasting in the summer of 2011, Magnús announced that he would be departing the role of Sportacus in late 2014 (after the end of the TV series), passing it on to Dýri Kristjánsson, who played Sportacus in all subsequent live shows. He also announced in late 2014 that he would depart from his position as CEO of LazyTown Entertainment.

Magnús was married to Ragnheiður Melsteð, whom he lived with for 24 years. The couple divorced in 2014. Magnús and Ragnheiður had a daughter and a son. Magnús also has a daughter with his former partner Halldóra Blöndall. In 2017, Magnús got engaged to Hrefna Björk Sverrisdóttir.

Since mid 2016, along with his partner, Hrefna Björk Sverrisdóttir, he has owned and managed ROK restaurant, a Scandinavian/seafood restaurant in Reykjavík.