He was also interim leader of the United Democratic Party for a brief period in the early 1980s.
Thompson was the UDP's nominee for the Belize House in the Belize City-based Mesopotamia constituency in 1974, but was defeated by the People's United Party incumbent, C. L. B. Rogers.
In January 1983 Thompson became Leader of the Opposition upon Theodore Aranda's departure from the UDP, serving concurrently as interim party leader until Sen. Manuel Esquivel was elected as Aranda's permanent replacement, with Thompson becoming deputy party leader.
Thompson served as deputy prime minister during the first Esquivel government from 1984 to 1989.
[1] Thompson was posthumously awarded the Order of Belize in September 2010.