Isaacs was born in Melbourne, the second son of Wolf Isaacs. In 1862 his family moved to Dunedin, New Zealand, where he was educated at Christchurch. After "about 25 years' residence in New Zealand", he returned to Victoria.
Victoria
In Victoria he was elected treasurer for the demonstration to celebrate Queen Victoria's Jubilee in 1887. In 1889 he was elected grand president for Australasia of the United Ancient Order of Druids; on his retirement from that office he was presented with a gold medal in recognition of 10 years continuous service on the board of directors.
Adelaide
He left Victoria in July 1899 to live in Adelaide and take the role of managing trustee of the estate of Ralph Raphael.
Isaac Isaacs was a member of the Adelaide City council for 30 years. He served as a councilor from 1902–1906, alderman from 1907–1915, mayor 1915-1917, and alderman again from 1917-1933. He also filled the role of chief magistrate during the war, and was chairman of the Finance Committee for more than 12 years.
Public Positions
He was president of the Justice Association, chairman of the Liberal Federation, a representative of the Municipal Tramways Trust, representative of both the City and the Suburban Local Boards of Health on the Central Board of Health, representative of the Adelaide Local Board of Health on the Metropolitan County Board under the Food and Drugs Act, member of the Metropolitan Infectious Diseases Hospital Board and held important positions in other organisations. He was also a land agent and an adjustor of fire claims.
Personal
He was a football enthusiast, a master of the St Andrews Masonic Lodge, a master of the Southern Cross Masonic Lodge, for three years chief president of the South Australian branch of the Australian Natives' Association, and president of the Adelaide Jewish Philanthropic Society. Isaacs married Zelinda Rosetta Raphael, daughter of Ralph Raphael, one of the State's pioneers. She was born in London in 1857 and was brought to Australia as an infant. She died at her home, "Quevedo", 2 Main North Road, Thorngate, on 10 July 1937, aged 80, and was buried at West Terrace Cemetery. She was survived by a son, R.R. Isaacs of Melbourne, and a daughter, Mrs. Mark Hains of Flaxley.
