Larsson was born as Karin Ejvor Johansson in Fellingsbro, Örebro, Sweden on 17 May 1904 to August Johansson and Anna Josefina Persson. She grew up on a farm called Tomasboda, located in Grönbo, which the family lived in from 1912 to 1920. They then moved to a dwelling named Sundbobruk, near Örebro.
Larsson worked at the university hospital in Uppsala, where she lived for a few years. She returned home to Sundbobruk to care for her father when he was taken ill. In July 1944, aged 40, she married Erik Larsson, and their only daughter, Kerstin, was born in September that year. They settled in Grönbo.
After Larsson was widowed in 1965, she again moved back into Sundbobruk, living there until her 90th birthday in 2004, when she moved into a nursing home in Lindesberg, Örebro. It was around this time that she became completely blind.
Following the 5 February 2014 death of Ellen Vestling, Larsson became Sweden’s oldest resident. She was not the oldest person born there, however, as U. S. resident Conrad Johnson was four months older. She died on 24 May 2014 at the age of 110 years, 7 days, with her successor as the oldest living person in Sweden being then-109-year-old Gulli Bergendahl.