Incumbent Ugandan President Yoweri Museveni has won the election, allowing him to extend his 30-year rule after the leading contender was arrested and social media was shutdown.
Mr Museveni claimed more than 60 per cent of the vote ahead of his opposition, Kizza Besigye, who had secured 35 per cent.
Besigye himself was under house arrest when Museveni was declared the winner, with heavily armed police standing guard near his residence on the outskirts of the capital, Kampala.
Museveni's ruling party, the National Resistance Movement (NRM), urged "all candidates to respect the will of the people and the authority of the electoral commission and accept the result. We ask all Ugandans to remain calm and peaceful and not to engage in any public disruptions."
The party released the statement shortly after the results were announced.
Mr Museveni, 71, has faced growing accusations from home and abroad for oppresing dissent and failing to stop extensive corruption.
Mr Besigye's arrest, his third of the week, contributed to violent confrontations in parts of the capital Kampala on Friday.
Police in riot gear had set off stun grenades and fired tear gas at Mr Besigye's supporters, who responded by hurling rocks and erecting street barricades. The streets were calm on Saturday morning.
US Secretary of State John Kerry called Mr Museveni on Friday to voice concern over Mr Besigye's detention, harassment of opposition figures and the shutdown of social media such as Facebook and Twitter.
The US State Department said in a statement: "(Mr Kerry) urged President Museveni to rein in the police and security forces, noting that such action calls into question Uganda's commitment to a transparent and credible election process free from intimidation."
Mr Besigye was arrested as he tried to hold a press conference at the headquarters of his Forum for Democratic Change (FDC) party to release their own poll results.
A senior FDC official said there were "glaring discrepancies" with official figures.
Another Museveni rival, former prime minister Amama Mbabazi, was put under house arrest, according to his spokesperson.
A NRM campaign spokesman for NRM said: "It appears as if our message that Uganda should maintain its path of steady progress for all, and not risk an untried and untested opposition, has resonated with the majority of Ugandan voters."
Brenda, 23, from Kampala said: "I have never seen another president and it seems it will be like that until he dies."
She refused to give her second name out of fears for her security.