Spencer was born in Hunston, Sussex, the third son of Cornelius Cosens, farmer, and his wife Ellen. In 1892 he emigrated to British Columbia, Canada, with his brother Arthur in order to look for gold. He did a variety of jobs then in 1894 formed a company of providers with his prother Sidney at Fairview and Camp McKinney. In 1898 he was a clerk at Vernon. He began screening motions pictures and met and married Mart Stuart Huntly who became his chief projectionist and business partner.
Spencer first arrived in Australia in 1905. He opened the Great American Theatrescope at the Lyceum Theatre in Sydney and eventually turned the Lyceum as a permanent picture theatre from June 1908.
He made a fortune exhibiting The Great Train Robbery in Australia and soon became the leading exhibitor in the country. He moved into production, establishing a permanent production unit under Ernest Higgins in 1908. Initially focused on documentary shorts and newsreels, he moved into funding dramatic feature films, starting with The Life and Adventures of John Vane, the Notorious Australian Bushranger (1910).
He was an early supporter of director Raymond Longford who directed The Fatal Wedding (1911) for Spencer. The success of this film enabled him to set up a ₤10,000 studio complex in Rushcutter's Bay, Sydney, where Longford made his next couple of features.
By 1912 he was the largest importer of films in Australia and helped popularise the medium in that country.
In 1911, Spencer had established a company, Spencer's Pictures Ltd with a nominal capital of ₤150,000. He went overseas for 12 months; while overseas, the board of Spencers voted to merge with Wests Ltd and Amalgamated Pictures resulting in the "combine" of Australasian Films and Union Theatres.
After the box office failure of The Shepherd of the Southern Cross (1914) Spencer was unable to persuade the combine to invest in drama production, and stepped back his involvement in the local industry.
Several of his films were released in the US by Sawyers Pictures; they were given new titles such as The Convict Hero, The Bushranger's Bride, Nell Gwynne, The Bandit Terrors of Australia and The Queen of the Smugglers.
In 1918 the Spencers were sued by the Combine for an alleged breach of contract. They settled out of court and left Australia.
Spencer returned to Canada with his wife, where he bought a ranch in British Columbia. In 1930, depressed after some financial reversals, he went on a shooting spree, killing his storeman and wounding another man, before drowning himself in a nearby lake. He left behind an estate worth $300,000.The Burns-Johnson Fight (1908)
Marvellous Melbourne (1910) – director
The Life and Adventures of John Vane, the Notorious Australian Bushranger (1910) – producer
Captain Midnight, the Bush King (1911) – producer
Captain Starlight, or Gentleman of the Road (1911) – producer
The Life of Rufus Dawes (1911) – producer
Dan Morgan (1911) – producer
The Fatal Wedding (1911) – producer
The Romantic Story of Margaret Catchpole (1911) – producer
Sweet Nell of Old Drury (1911) – producer
The Midnight Wedding (1912) – producer
The Bushman's Bride (1912) – producer
The Tide of Death (1912) – producer
Australia Calls (1913) – producer
The Shepherd of the Southern Cross (1914) – producer