William Edward Marmion (22 October 1845 – 4 July 1896) was an Australian politician. He was a member of the Western Australian Legislative Council from 1870 to 1890, and a member of the Western Australian Legislative Assembly from 1890 to 1896.
Marmion was born in Fremantle, Western Australia. Having worked from the age of 16, he started his own business at the age of 21, W. E. Marmion & Co., which came to have interests in pastoral, pearling and maritime activities. He also formed mining companies after the gold was discovered in Yilgarn. He married Anna Mary Gibbons in 1870, with whom he would have three sons and six daughters.
When Western Australia introduced representative government in 1870, Marmion ran unsuccessfully for the Legislative Council seat of Fremantle. He was instead made an unofficial member of the chamber, and became an official member of the Legislative Council when he won the seat of Fremantle in 1873. Marmion transferred to the Legislative Assembly, when that body was created in 1890, winning the district of Fremantle. He was made commissioner of crown lands and minister for mines that same year by Premier John Forrest. According to R. T. Appleyard, "[u]nder Marmion the gold-mining industry became the economic vehicle which transformed a quiet backwater into a colony attracting enormous international interest. He had financial acumen and understood the infrastructure requirements needed to service rapidly increasing trade and population."
In 1894, some newspaper editors accused Marmion of a conflict of interest because of his dual roles as minister and leading business investor. Marmion chose to resign his commission as minister. His action was met with surprise, with "some seeing it as consistent with his integrity."
Marmion died suddenly of liver disease on 4 July 1896. It was reported that more people attended his funeral than any previous funeral in Western Australia to that time, and that the streets of Perth were lined with thousands. A large Celtic cross was erected in Mayor's Park, Fremantle as a monument to him.