He was born in Halifax, the son of Alexander Forrester. He was educated at the Halifax Grammar School and, after completing his schooling, joined the British Army. Forrester served during the War of 1812. After the war, he became a dry goods merchant in Halifax. In 1813, he married Elizabeth Martin. Originally a supporter of Joseph Howe, Forrester later withdrew his support because he felt that Howe had made too many compromises to become part of the coalition government. During the financial crisis of 1837, Forrester sued the Bank of Nova Scotia for refusing to redeem paper money for coin. He also lobbied for Halifax's incorporation as a town.