Per Mathiesen was a member of the Norwegian men’s gymnastics team, which won an Olympic gold medal in the all-around free system event. He graduated in pharmacy in 1909. In 1930, he took over the Sannesund pharmacy in the Sarpsborg region. After running the pharmacy in the 1930s and 1940s, he applied to the Norwegian Storting for compensation for income losses resulting from the temporary closure of the pharmacy. The reason for this closure is unknown, however. A few months prior to his Olympic appearance, he married Ragnhild Kristofa Waldeland. With her, Per Mathiesen had two daughters and a son. After the death of his first wife, he remarried in 1937. With his second wife, Berta Pedersen, he had one more son.