Frommelt was born on 14 March 1895 in Schaan as the son of carpenter Lorenz Frommelt and Magdalena Vogt. He attended college in Stans and from 1920 he studied theology in Chur. He worked as an art teacher between 1920 and 1922. He was as a pastor in Triesen from 1922 until 1933.[1]
In 1930 he had supported the approval for the building of a 23km long inland canal to increase the percentage of arable land within the country and to create job opportunities within the country, which was approved in 1930, started construction in 1931 and then completed in 1943.[5][6]
The Progressive Citizens' Party participated in the coalition government formed in the wake of World War II to prevent government deadlock and help retain Liechtenstein's neutrality overseen by Franz Joseph II.[7][8] As a result, Alois Vogt of the Patriotic Union was appointed to became Deputy Prime Minister under Hoop for the rest of his premiership and Frommelt resigned, but retained his position as President of the Landtag of Liechtenstein.[4][3]
He played a key role in thwarting the German National Movement in Liechtenstein (VDBL) when they attempted a coup in 1939 by blocking their telephone lines and convincing marchers to stand down. He was a fierce opponent of National Socialism.[1][9] Frommelt resigned all of his political positions in 1945, near the end of World War II.[1] Due to death reasons, he did not become a pastor again but instead dedicated himself to becoming an artist and photographer.[10] He published approximately 1,700 photographs throughout his lifetime.[11] While he was no longer active in politics he still periodically gave advice to Alexander Frick on stamp policy and created many designs of the stamps himself.[12] He played a role in the re-establishment of the Liechtenstein National Museum in 1954.[1]
Frommelt died on 7 October 1975, at the age of 80.[1] He is buried at the cemetery in Vaduz.