Richard John Augustus Longworth was born in Charlottetown, Prince Edward Island, on 7 August 1857, one of six children to John Longworth and Elizabeth Tremaine. Although his baptismal name was Richard, he was more commonly known by his middle name John. Educated at King's College, he became a lawyer in Charlottetown, ultimately taking the position of Prothonotary of the Supreme Court of Prince Edward Island. On 4 October 1888, John married Louise Caroline Palmer in Charlottetown, and they had six children: Ethel Constance, Mabel Elizabeth, Frederick John, Dorothy Amelia, Louise Joan, and Helen Caroline.

John A. Longworth was also involved with the local militia, receiving commissions to No. 2 Battery Prince Edward Island Provisional Brigade of Garrison Artillery, first as Lieutenant in June 1884, and then as Captain in September 1887. In 1895, he took up the position of Lieutenant Colonel in the 4th Prince Edward Island Regiment Canadian Artillery. He also represented Prince Edward Island in the Canadian Jubilee Contingent that visited England in 1897 to take part in Queen Victoria's Diamond Jubilee Procession.

John A. Longworth died on 5 November 1909.