Lilletun was born in Western Vossestrand, now a part of the municipality of Voss. His father owned a farm and also worked as a mailman. Lilletun was raised as a Pentecostal, and his family always tithed to the religious community.
After his mandatory 8-year primary education, Lilletun's family was unable to finance attendance at a higher level of school with an academic track. Lilletun worked as an apprentice at a local merchant and attended various trade schools. In 1974, he opened his own retail store that went bankrupt within a few years. He was subsequently convicted of negligence in his accounting practices and sentenced to a 55-day prison term, which he served.
He attributed this experience with a new outlook on life, and from 1975 to 1988 he worked for the municipality of Vennesla on issues related to youth. In 1982, he ran for election as the mayor of Vennesla, but lost in a landslide defeat. During this time he also moved from the Pentecostal movement to the Church of Norway.
Political career
Representing the county of Vest-Agder, he served as a deputy member of the Norwegian parliament from 1981 to 1985, and as an elected member from 1989 until his death. In the spring of 2005 he took sick leave, and his deputy Sigmund Kroslid filled in for him. After his death he was replaced by Dagrun Eriksen.