He received his candidate of law degree from the University of Copenhagen in 1882, and then served on Suðuroy as a deputy local administrator from 1883 to 1894 and as a local administrator from 1894 to 1920. He was a council member in the Municipality of Froðba (Froðbiar kommuna; now the Municipality of Tvøroyri, Tvøroyrar kommuna) from 1888 to 1905, and mayor of the municipality from 1889 to 1905. Effersøe also served as a postal official in Trongisvágur from 1883 to 1905, as a board member of the bank Færø Amts Sparekasse from 1918 to 1923, and as the claims commissioner for Suðuroy from 1894 to 1905.