In 1955 Crabbe joined the Attorney-General's Department of Ghana as an Assistant
Crown Counsel. Together with the New Zealand lawyer Fred Boyce, he drafted the legislations, Ordinances and Acts of Parliament which were passed by the National Assembly on the eve of 6 March 1957 for Ghana's Independence. On 1 June 1958, he was promoted as a first
parliamentary counsel, becoming the first African to achieve the rank of a parliamentary counsel (state attorney). He was appointed Head of Drafting at Ghana's
Ministry of Justice and was responsible for producing the legislations to be passed by Ghana's early
National Assembly. In 1963, president
Nkrumah sent him on a mission to Uganda where he was made a first parliamentary counsel and constitutional advisor to the
Uganda government and drafted the 1966 Ugandan constitution. In August 1968, he was appointed interim electoral commissioner of Ghana to conduct the 1969 elections on his return from Uganda. Crabbe set up Ghana's first-ever electoral commission. In addition, he served as special commissioner to the 1969 Constitutional Commission and a legislative draftsman to the 1969 Constituent Assembly which drafted the 1969 Constitution of Ghana. Crabbe was chairman of the 1979 Constituent Assembly of Ghana, which drafted the 1979 Constitution of Ghana. Crabbe was co-chair of the Coalition of Democratic Election Observers Ghana (CODEO), an agency under the Ghana Centre for Democratic Development (CDD-Ghana), which independently monitors electoral processes. In 2002, Crabbe worked with the Constitutional Review Commission of
Kenya and was leader of the group of draftspersons who drafted the Kenya Constitution. In the same year, he did work the Zambian Constitutional Commission for the drafting of the Zambian Constitution. Crabbe worked with the Fiajoe Review Commission for the review of the 1992 Constitution of Ghana and also worked with Justice
P. N. Bhagwati, former Chief Justice of
India and Justice
Kayode Eso of the
Supreme Court of Nigeria to advise on the setting up of the Constitutional Court in
South Africa. In January 1999, Crabbe was appointed by the Ghanaian government as Commissioner of Statute Law Revision. He held office until 2014 at the Ghanaian Ministry of Justice and in this office revised the Laws of Ghana from 1852 to 2004 in seven volumes before retiring from public office. ==Work as a Judge==