Tawharanui Peninsula is a finger of land projecting into the Hauraki Gulf from the east coast of the much larger North Auckland Peninsula of New Zealand. It separates Omaha Bay to the north from Kawau Bay and Kawau Island to the south. The nearest sizable town is Warkworth.
Tawharanui Regional Park covers 588 hectares of the peninsula’s land and Tawharanui Marine Reserve covers the northern coastal sea. Both are administered by Auckland Council  which also owns the regional park.
Geologically the peninsula consists of Waitemata Sandstone on top of folded and uplifted greywacke.
Māori lived in the area for over 800 years. The Māori name Tawhara-nui refers to „the abundant bracts of the kiekie vine“. Until the 1870s, the park was occupied by a small hapu (sub-tribe) of the Te Kawerau people called Ngati Raupo. The people lived mainly around the catchment of the Mangatawhiri Stream. A significant pā, Oponui, was near the entrance to the park and above the stream outlet was Pa-hi (meaning „lofty fortified settlement“). Tawharanui provided a large variety of marine and forest resources. This was celebrated in the saying, „He wha tawhara ki uta; he kiko tamure ki tai“ – „The flowering bracts of the kiekie on the land, the flesh of the snapper in the sea“. Waikokowai (Anchor Bay) provided a valued source of kokowai or red ochre, which was used for decorative and ceremonial purposes.
Tawharanui was sold by the Māori owners in 1873–1877 and developed as a farm by the Martin, Jones and Young families. Kauri timber was milled and manuka cut for firewood for many years. Shingle was extracted for a hundred years, creating the Jones Bay Lagoon. Nine vessels were wrecked on the Tawharanui coastline between 1871 and 1978. Anchor Bay is named after the anchor of the Phoenix, wrecked in 1879. The Auckland Regional Authority, forerunner of the Auckland Council, purchased the parkland from the Georgetti family in 1973.
The park combines a „mainland island“ sanctuary for the conservation of native plants and animals with farmland and public recreation areas. The park is mostly grazed pasture with manuka scattered throughout and patches of coastal forest. The most significant area of coastal forest is in the central eastern part of the park where kauri and rimu dominate the ridges, with puriri, taraire, tawa and, less often, rewarewa and nikau in the valleys. Elsewhere there are totara, kahikatea, pohutukawa, cabbage trees, karaka and New Zealand flax.
The mainland island was created by the construction of a 2.5 km pest-proof fence across the peninsula in 2004. This was followed by an aerial drop of poison later in 2004 which eliminated black rats, brown rats, feral cats, possums, weasels, stoats and ferrets. Introduced pests remaining in the sanctuary are mice, rabbits and hedgehogs. The Tawharanui Open Sanctuary Society Inc. (TOSSI) assists Auckland Council with the sanctuary by fundraising and volunteer work.
Sixteen species of native land birds and 15 species of native coastal birds have been recorded in the park. Wetland birds include the Australasian bittern, spotless crake and fernbird. Coastal birds include the New Zealand dotterel, blue reef heron and variable oystercatcher.
Tāwharanui Marine Reserve was established in 2011. The marine reserve replaces the Tawharanui Marine Park, which was established in 1981 as New Zealand’s first Marine Protected Area. It covers approximately 395 hectares, from Mean High Water Mark out to half a nautical mile into the sea, along three kilometres of the coastline. Regulations administered by the Ministry of Fisheries prohibit the taking of any marine life. The diverse coastline contains a range of subtidal habitats, including reefs with overhangs, tunnels and caves. Schools of red moki, blue maomao, spotty, red mullet and koheru are common. North Island brown kiwi was reintroduced into the area.Cetaceans such as bottlenose dolphin and orca or other species also visit the waters nearby.