Planinc was born on 8 September 1925 in Ljubljana. After graduating from the Ljubljana teaching school and attending evening classes in drawing (M.Pregelj), he studied painting at the Academy of Fine Arts in Ljubljana (1949-1954, graduating from the class of Prof. Gojmir Anton Kos), where he also pursued his post-graduate studies in the class of Prof. Marij Pregelj (1954-1956) who encouraged him to take up illustration. He stayed in Paris on two occasions (in 1961 - Lhote School of Painting, and in 1969) on a Moša Pijade scholarship. From 1974 until his retirement in 1985 he was employed at the Ljubljana Academy of Fine Arts (appointed full professor of painting in 1985). He was a member of the BE-54 group (from 1958 on) and Group 69 (Grupa 69; from 1972 on). He received the Levstik Award for Children's Illustration several times (1958, 1959 and 1963). In 1964 he received the Prešeren Fund Award and in 1984 the Jakopič Award for Painting. His work includes painting (since 1960 his series - in mixed media based on tempera - observe the experience of Surrealism), drawing, illustration (less since 1980) and book design.