He earned 30 caps for the Denmark national speedway team.

[1] Thomsen was a Speedway World Team Cup winner with the Denmark national speedway team in 1978, 1981 and 1983.

Thomsen first rode in the United Kingdom with the Wolverhampton Wolves during the 1974 British League season[2][3] where he spent four years steadily improving his average.

[4] In 1978, he was signed by Len Silver for the Hackney Hawks in a swap deal with Dave Morton, later becoming team captain in 1980.

When Hackney closed at the end of the 1983 season, he moved to Poole Pirates for the 1984 season and rode for Swindon Robins in 1986.