[1] Marmon was born in Sydney, New South Wales, the son of a convict stonemason of Irish descent.
If Marmon's own account is to be believed, he first went to sea on a whaling vessel at 5 years of age, visiting Bay of Islands New Zealand in 1805 before returning to Sydney.
He became fluent in Māori and travelled on the Ngāpuhi raids on the Hokianga under the leadership of Hongi Hika.
He attempted unsuccessfully to convince Hokianga Maori not to sign the Treaty of Waitangi in 1840,[1] but later during the period now known as the Flagstaff War he and the Hokianga Māori supported the British troops and Tāmati Wāka Nene;[3] with Marmon himself recovering the bodies of the Europeans slain during the Battle of Ohaeawai.
[1] His relationships with the European population were always tainted by the suggestion that he had taken part in cannibal feasts in his early raids with the Māori.