From about 1846, Isaacs practiced as a barrister on the island of Antigua in the West Indies, during which time he was a member of the Legislature.

For a period, he filled the role of acting Chief Justice and for several years was Chancellor to the Bishop.

[1] In October 1855, Isaacs and his family sailed from Liverpool for Australia aboard the clipper ship Schomberg on her maiden voyage, which was wrecked near Cape Otway on 27 December 1855.

[4] In 1865, he was elected to the New South Wales Legislative Assembly for Yass Plains, serving until his retirement in 1869.

Isaacs was appointed as Solicitor-General in the second government of James Martin in 22 January 1866, and continued in that role until 26 October 1868.