He served as the third Prime Minister of Saint Vincent and the Grenadines, and is the former longtime leader of the opposition and former president of the New Democratic Party (NDP) after resigning in 2016.

[2][3] Eustace was a Member of Parliament (MP) for the constituency of East Kingstown in the House of Assembly of Saint Vincent and the Grenadines from 1998 until his retirement in 2020.

At the age of 27, Eustace became the youngest permanent secretary in St. Vincent and the Grenadines when he was so assigned to the Ministry of Agriculture.

For roughly one year after his departure he fished, literally, the waters off Edinboro, until Sir William Demas flew into St. Vincent to recruit the young economist into the Caribbean Development Bank.

[9] In 1998, he resigned from the public service and ran for political office, winning the East Kingstown parliamentary seat previously held by fellow party member Carlyle Dougan.

Later that year he was offered the post of Deputy Secretary General of the British Commonwealth Secretariat in London, which he declined.

In 2016, Eustace resigned as both leader of the opposition and President of the New Democratic Party after holding the two positions for 15 years.