He served as a deputy representative to the Norwegian Parliament from Bergen during the terms 1965–1969 and 1969–1973. From August to September 1963 he was Minister of Wages and Prices during the short-lived centre-right cabinet Lyng. He became Minister of Finance from 1965 to 1971 during the cabinet Borten. In December 1972, Myrvoll joined the New People's Party which split from the Liberal Party over disagreements of Norway's proposed entry to the European Economic Community. He was elected to Norwegian Parliament for this party in 1973, this time from Hordaland as Bergen had ceased to be a county and as such constituency.
On the local level Myrvoll was a member of the executive committee of Bergen city council from 1947 to 1955 and 1974 to 1975. He served as mayor from 1972 to 1973.