Jakaya Kikwete, the foreign minister, has promised to continue the free-market policies of Benjamin Mkapa, who is stepping down after two terms as president in which he has consolidated the east African nation's reputation for stability.
The nearest rival, the opposition Civic United Front, took only 11% of the vote.
Kikwete, 55, and Mkapa's ruling Chama Cha Mapinduzi (CCM or Party of the Revolution) has held power for 40 years in Tanzania, one of Africa's biggest per-capita aid recipients with a population of 35 million on the mainland and Zanzibar islands.
CCM hegemony has ensured political stability, which has been the basis of good relations with the West.
But it has also frustrated Tanzania's small and divided opposition parties, who say their country remains a de facto one-party state despite the introduction of multi-party politics in the early 1990s.
Unrest in Zanzibar, a semi-autonomous archipelago in the Indian Ocean, which is a stronghold of the Civic United Front party, marred Wednesday's voting.