Educated locally up to West African school certificate in 1956. He joined the army on March 17, 1958, was commissioned after a course at Sandhurst on December 15, 1960. He did further advanced military courses including two signals courses at Catterick, Britain and an associate officers course in the USA.
Erskine was commissioned at the Royal Military Academy, Sandhurst, in December 1960 into the Signal Corps of the Ghana army. Erskine has served in various capacities with the Ghana army. He was Commanding Officer of the Ghana Signals Regiment and later Director of Communications with the Ghana Ministry of Defence. He later became Director for Operations and Planning at the same Ministry from 1971 to 1972. He was the Chief of Army Staff briefly between January and February 1972. He again held the same position from February 1973 to April 1974.
Erskine served as the Chief of Staff and Deputy Force Commander of the United Nations Emergency Force Two (UNEF 2) from 1974 to 1976 in Egypt. He was then appointed as the Chief of Staff of UNTSO in Israel between January 1976 and April 1978. He subsequently became the first commander of the United Nations Interim Force in Lebanon (UNIFIL) between 1978 and 1981. Erskine again occupied the position of Chief of Staff of UNTSO and was also the United Nations Secretary General's Representative for Matters relating to UN Peacekeeping Operations in the Middle East from February 1981 to May 1986.
Erskine was one of the founding members of the People's Heritage Party (PHP). He was the party's presidential candidate during the 1992 Ghanaian presidential election. He came fifth with 1.7% of the vote. The PHP later merged with the National Independence Party to form the People's Convention Party (PCP) in 1993.
Erskine was one of the nine members of the National Reconciliation Commission which were appointed by the President of Ghana, John Kufuor in consultation with the Council of State of Ghana. The commission was to investigate human rights abuses committed during the five military regimes which have ruled Ghana.
General Erskine is the Chairman of the Opportunities Industrialization Centre Ghana Accra Local Programme Committee. He has been a member of the Pugwash council since 1992 and was a participant at the 50th Pugwash conference which deliberated on "Eliminating the Causes of War". He served as the Chairman of the Ghana Action Network on Small Arms (GANSA)in 2002.