Lewis Acker was born probably in New York, in the United States, some time between 1813 and 1817. His father, variously recorded as a mariner and as the possessor of a substantial estate, allowed him to go to sea in the hope that this would help to settle a lad regarded as rather wild. Acker came to New Zealand about 1831 as harpooner on an American whaler. He eventually took his discharge in Sydney, returned to New Zealand and may have been engaged at one of the Cook Strait whaling stations, since he is said to have been one of the whalers who assisted Taranaki Maori in the defence of Ngāmotu against Pōtatau Te Wherowhero in 1832.
By 1834 Acker had moved to Foveaux Strait and purchased 600 acres in Halfmoon Bay, Stewart Island. In the same year he named New River (Ōreti River), on the coast of Southland, after he and a boat crew had been forced to spend a night on Point Island in the river's mouth. He spent some time in the employ of Captain John Howell, manager of a whaling station at Jacobs River (Aparima River), but left in 1839 when he agreed to manage a station at Centre Island in Foveaux Strait for George and Edward Weller. Perhaps because of financial difficulties the Wellers failed to deliver the necessary supplies and the venture did not go ahead.
It may have been as a result of this disappointment that Acker turned to building and repairing boats, a business that necessitated journeys to Otago Harbour. Here he met Mary Pi, daughter of Kaniua and Hine Pipiwai of Kaiapoi. She had apparently been forced to leave Kaiapoi pā when it was under threat of attack by Te Rauparaha. She followed Acker south, and they were married by the Reverend James Watkin on 4 March 1844; their two-year-old daughter, Catherine, was baptised at the same time. They lived in a stone house Acker had built on Stewart Island, seemingly in imitation of his childhood home. Acker himself quarried the stone in the New River district and transported it across Foveaux Strait. In this house, the remains of which may still be seen, Lewis and Mary Acker raised nine children.
Acker's activities in this period cannot be stated with precision. He may still have been engaged in boatbuilding and must certainly have been in some maritime occupation, since in 1857 he was gazetted as pilot for New River and Foveaux Strait. He was also trading in his schooners Fanny and Mabel Jane.
Some time in the early 1860s Acker left Stewart Island and took up farming at Otatara, near Invercargill. Mary Acker died about this time, and on 5 September 1863 Lewis Acker married Jane Stuart at Invercargill. They had five children, two of whom drowned in 1882. In 1864 the government purchased Stewart Island and Acker, who had failed to submit a claim for the land he had bought, was dispossessed of his holding. For a time he managed a sawmill he had acquired for £700, an occupation which ended with the mill's destruction by fire.
Lewis Acker died at Otatara Bush, Invercargill, on 11 July 1885.