Romme attended the Amsterdams Lyceum from June 1909 until June 1914 and applied at the University of Amsterdam in June 1914 majoring in Law and obtaining a Bachelor of Laws degree before graduating with an Master of Laws degree in July 1919. Romme worked as a lawyer in Amsterdam from September 1919 until June 1937. Romme also worked as a trade association executive for the Catholic Employers' Association from November 1919 until December 1924 and was a contributing editor for the magazines Het Patroonsblad and De RK Werkgever from February 1920 until December 1924. Romme served on the municipal council of Amsterdam from April 1921 until June 1937 and served on the Provincial Council of North Holland from June 1935 until June 1937. Romme also became active in the private sector and public sector and occupied numerous seats as a corporate director and nonprofit director on several boards of directors and supervisory boards (Brill Publishers, Elsevier and the Concertgebouw) and served on several state commissions and councils on behalf of the government (Mine Council and the Council for Culture). Romme also worked as an associate professor of labour law at Tilburg University from 1 January 1933 until 1 January 1935 and as a distinguished professor of Labour law, administrative law and constitutional law and at Tilburg University from 1 January 1935 until 24 June 1937.
Romme again worked as a lawyer in Amsterdam from January 1940 until June 1946. During the German invasion of the Netherlands on 10 May 1940, the government fled to London to escape German occupation. During World War II Romme continued to work as a lawyer. In December 1941 Romme was arrested and detained in Amsterdam and was released in January 1942. On 4 May 1942 Romme was arrested again and detained in Kamp Sint-Michielsgestel but was released four days later on 7 May 1942. Following the end of World War II, Romme became actively involved in politics again, and was one of the primary initiators for reforming the Roman Catholic State Party. On 22 December 1945 the party was renamed as the Catholic People's Party, and as one of its co-founders, Romme was selected as the first Leader of the Catholic People's Party and the lead candidate of the party for the 1946 general election on 10 January 1946. The Catholic People's Party had 31 seats in the House of House of Representatives previously held by the Roman Catholic State Party and won slightly, gaining one seat. It remained the largest party and now had 32 seats in the House of Representatives. Romme was elected again to the House of Representatives and became his party's parliamentary leader in the House on 4 June 1946. Romme served continuously as party leader and parliamentary leader for the next 15 years and was lead candidate for the 1948, 1952, 1956 and 1959 general elections.