An Aliyev victory was widely seen as a foregone conclusion with the Caspian state's downtrodden opposition unable to mount a serious challenge to his authoritarian rule.
In power for 15 years, Aliyev received 86.1 per cent of the vote, the Central Election Commission said in a statement, after 67.3 per cent of votes were counted.
Turnout was 74.5 per cent, the statement added.
Aliyev's position has been boosted in recent years by the steady influx of petrodollars into his government's coffers.
Opposition parties in the tightly controlled Caucasus nation have said the elections are a sham and accused the authorities of preparing to rig the vote.
Fire kills 25 in drug treatment centre in Azerbaijan
They have also condemned Aliyev's surprise — and unexplained — decision to hold the election six months ahead of schedule, saying it was aimed at shortening the campaign period and hampering efforts to prevent vote-rigging.
"All previous elections in Azerbaijan were falsified and held with blatant violations of the electoral law. These elections will be no exception," said the executive secretary of the opposition Republican Alternative Movement, Natig Jafarli.
But authorities rejected the criticism, insisting the vote was free and fair.
"Azerbaijan is on a firm and irreversible path of democratic development. A free, open and transparent environment has been created in Azerbaijan for the presidential elections," foreign ministry spokesman, Hikmet Hajiyev, told AFP.
"All the candidates enjoy equal rights and opportunities," he added.
Earlier in the day at a polling station in the capital Baku, 38-year-old schoolteacher Elmira Balayeva said she had voted for Aliyev because he was the only candidate capable of steering the country towards economic wellbeing and political stability.
"There is no alternative to Aliyev. Only thanks to him is Azerbaijan a stable country with a strong economy," she said.
But for Natig Veliyev, a 27-year-old student who did not turn out to vote, "the elections are pure farce."
"We have never seen free elections in this country. Aliyev simply extends his reign again and again."
Turnout was 68.7 per cent, according to the government-commissioned exit poll, but activists earlier questioned official participation figures.
Aliyev, 56, was first elected in 2003, after the death of his father Heydar Aliyev.
A former KGB officer and communist-era leader, Aliyev senior had ruled Azerbaijan with an iron fist since 1993.
Ilham Aliyev was re-elected in 2008 and 2013 in polls that were denounced by opposition parties as fraudulent.
Pakistan set to export its manpower to Azerbaijan
In 2009, he amended the country's constitution so he could run for an unlimited number of presidential terms, a move criticised by rights advocates.
In 2016, Azerbaijan adopted fresh controversial constitutional amendments, extending the president's term in office from five to seven years.
The changes drew criticism from Council of Europe constitutional law experts as "severely upsetting the balance of powers" and giving the president "unprecedented" authority.
Cementing his family's decades-long grip on power, the president last year appointed his wife Mehriban Aliyeva as first vice president.
Apart from the incumbent president, seven candidates ran in the poll — all low-profile figures who barely carried out any campaigning.
Supporters have praised the Aliyevs for turning a republic once thought of as an ex-Soviet backwater into a flourishing energy supplier to Europe.
But critics argue they have crushed opposition and used their power to fund a lavish lifestyle for themselves and their family. Aliyev has denied accusations of rights abuses and corruption.
Some 5.2 million people were registered to vote in polls monitored by international observers from the Organisation for Security and Cooperation in Europe.
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ