William was born in Sligo County, Ireland to Peter and Catherine (Lytle) Shannon. Around 1845, the family moved to Lindsay, Ontario and began farming. William went to public school in Lindsay and wanted to become a farmer.
In May 1862, he arrived in California by the Panama route. In 1963, he arrived in New Westminster, BC after working his way up the coast. He became a partner to his brother, Thomas, in a road contracting business. They built Mary Street in New Westminster.
In 1864, he and William Parson bought land on the North side of Lulu Island. He started the first trading post in the south end of the Okanagan country and Kootenay in 1865. In 1866, he took charge of a small party, who started from Big Bend mines on the Columbia River, in order to explore the country. He sold out his partnership.
From 1866 to 1869, he mined at Big Bend, Columbia River, Goldstream, McUllis, French Creek, and Camp Creek. He helped to improve the method of saving fine gold.
In 1868, he began stock raising and farming with his brother Thomas David in Chiliwack. The Shannon family was the first to import Ayreshire cattle from Scotland to BC and introduced purebred Berkshire pigs and Clydesdale horses. Thomas David was the first man to bring New Hampshire chickens to BC.
In 1869, he began fur trading in various areas. He then became interested in cattle ranching in 1870. William drove the first large freight wagon to the Cariboo Mines, Williams Creek, and Barkerville in 1871.
In 1873, he helped form the first municipality on the mainland at Chilliwack, serving as a member of the council. In 1874, he helped the government compose and draft the first municipal act in BC for Chilliwack. Subsequently, he served as a member of the first council.
William was involved in the lumber business from 1876 to 1881. In 1881, he built a farm on the east side of Granville (south of 57th).
He married Eliza Jane McIndoo in 1886. In 1887, he settled in Vancouver and became a real estate broker. His first partner was J.Z. Hall.
His son William Lloyd was born on October 23, 1887. He visited the Squamish Valley in 1888 and declared it to be "fertile and good for settlers". He bought a lot of land in the Valley including the area of Shannon Falls and Darrell Bay.
In September 1888, he formed a partnership with Charles McLachlan in Real estate and insurance as financial agents. The Squamish Valley Hope Raising Co. Ranch was formed in 1891 and he became President.
In July 1894, the Foreman of roads in South Vancouver (J. McRorie) was murdered on Shannon's Place.
In 1899, he wrote "British Columbia and its Resources" and served on the first Grand Jury held in Vancouver.
In 1906, thirty Fraser Valley farmers followed Shannon to farms on Graham Island in the Queen Charlottes. In 1907, William joined George Martin in the firm of Martin and Shannon, owners of land on Sea Island and Potlatch Creek.
William sold 300 acres of land to Mr Sullivan of Surrey for $16,000 on August 2, 1909. He also sold a 40 acre farm to Jonathan Rogers of Rogers Building for $50,000 in cash in 1928.
His son William died on December 26, 1922. William Shannon died on on February 2, 1928 and was buried in Internment Ocean View Burial Park. His wife died at age 77 on June 16, 1932.
Memorials: Shannon Falls, Shannon Park (property part of old Shannon farm. Owned jointly by Park and School Board), and Shannon Road.