William Parker (1800-1873) was born in Dumfriesshire, southern Scotland, one of eleven children born to John Parker (c1779-1856) and Jannet Lockerby (1780-1849). By 1823 William Parker was a mate on the Lindsey, a three-masted 254-ton sailing ship of which his maternal uncle, William Lockerby (1783-1853), was owner-captain. The Lindsey was one of two ships hired to bring British officers and seamen to Brazil for service, and on 27 January 1823 she set sail from Liverpool, with 6 officers and 125 men, all officially free settlers in Brazil; William was amongst the crew. Two months later William left his post, volunteered for the Brazilian navy, and on 3 April he was appointed a second lieutenant on Thomas Lord Cochrane's flagship, Pedro I; Cochrane (1775-1860) had been invited by the Brazilian government to lead a naval campaign to expel the Portuguese. John Pascoe Grenfell (1800-1869) was also amongst Cochrane's men. Parker rose throughout the ranks and was involved in various naval battles against the Portuguese and Argentinians. He was promoted to Lieutenant in October 1825 and received his first command in August 1827 on the schooner Bella Maria.

In 1829 William Parker and John Pascoe Grenfell both married daughters of Antonio Masini (c1765-1813), an Italian-born shipowner living in Montevideo, Uruguay. Whilst Grenfell married Maria Dolores Masini (1804-1860) at the beginning of 1829, Parker married her sister, Maria Engracia (1800-1843), in March of that year. Parker and Maria Engracia had four children: Flora (1830-1904), Guillermo (1831-1864), Maria Engracia (1832-1901), and Augusto (1836-1902). Originally settling in Rio, Brazil, the Parker family set up home in Montevideo around August 1831.

William Parker retired from the Imperial Brazilian Navy due to ill health in January 1867. Having reached the rank of Vice-Admiral, he became a full Admiral on his retirement. He died on 27 March 1873.