Maning is the eldest son of moderately wealthy, Protestant Anglo-Irish parents. His father, Frederick Maning, emigrates to Van Diemen’s Land in 1824 with his wife and three sons to take up farming. Young Maning becomes a skilled outdoorsman and builds up the physical strength to match his six-foot, three-inch stature. In 1829, his father becomes a customs officer in Hobart and moves there with his family. By 1832, Frederick leaves home to manage a remote outpost in the north of Tasmania. Soon after, he decides to pursue his fortune in New Zealand.
Maning arrives in the Hokianga area on June 30, 1833, and lives among the Ngāpuhi Māori people. With his physical skills and great stature, as well as his considerable good humor, he quickly gains favour with the tribe. He becomes known as a Pākehā Māori (a European turned native) and his arrival in New Zealand is the subject of the first chapters of his book Old New Zealand.
In 1837, he sells his property and returns to Hobart. He returns to Hokianga in March 1839 and in September purchases 200 acres for a farm at Onoke. He builds a house there that is standing until destroyed by fire in 2004. He takes a Māori wife, Moengoroa, and they have four children.
In 1840, Maning acts as a translator at meetings about the Treaty of Waitangi, and he advises the local Māori to not sign. His vocal opposition to the Treaty is primarily because he has settled with the Māori precisely to escape from the restrictions of European civilisation. He fears that the introduction of European style law will put a damper on his lifestyle and on his entrepreneurial trading activities. He warns the Māori that European colonisation will degrade them. Governor William Hobson counters by telling the Māori that without British Law, lawless self-interested Europeans without any regard for Māori rights will soon take all their land. Maning’s book Old New Zealand is, in part, a lament for the lost freedom enjoyed before European rule.
In 1845–1846, during the Māori Wars, Maning sometimes uses his influence with the Māori to intercede on behalf of settlers. He also organises supplies to the government’s Māori supporters. However, he writes his second book, History of the War in the North of New Zealand against the Chief Heke, from the perspective of an imaginary supporter of Hōne Heke, who is one of the principal antagonists opposing the government.
Through the 1850s, Maning primarily occupies himself with timber and gum trade. In the early 1860s, he retires from business activities. In 1865, he enters the public service as a judge of the Native Land Court, where his unequalled knowledge of the Māori language, customs, traditions and prejudices is of solid value.
Maning retires in 1876 although he helps conduct a major land court hearing at Taupo in 1881. He becomes estranged from his children in his later years. In November 1882, he goes to London for an operation, however, he dies there on July 25, 1883 of cancer. At his wish, his body is taken back to New Zealand and buried in December 1883, in the Symonds Street Cemetery in Auckland.
Maning is chiefly remembered as the author of two short books, Old New Zealand and History of the War in the North of New Zealand against the Chief Heke. Both books have been reprinted many times and have become classics of New Zealand literature.