Born in Copenhagen, she spent her childhood in Helsingør where her father, Hans Julius Mydtskov, was also a photographer.
In 1937, the family moved to Copenhagen where her father, who had taken photographs at the Royal Theatre since 1930, opened a studio in Store Kongensgade.
In 1954, she began working little by little as a theatre photographer, first substituting for her brother Jørgen, finally taking over his position when he retired in 1972.
Among her best-known theatre photographs are the actors Poul Reument and Bodil Kjer (1955) and the ballet dancer Anna Lærkesen (1963).
But she also photographed Bodil Ipsen, Clara Pontoppidan, Mogens Wieth, Ebbe Rode, Ghita Nørby, Jørgen Reenberg, Lise Ringheim, Henrik Moritzen, Erik Mørk and Susse Wold.
In 1991, she presented "Portraits of a Queen" at the Auktionshuet Bukowski and in 1997, participated in the travelling exhibition Selskaber (Companies).
Rigmor Mydtskov took the initiative to arrange many photographic exhibitions, often as external examiner or judge.