Aliyev, first elected president in 2003, two months before his ailing father and long-serving leader Heydar died, cemented his position with two referendums - one in 2009 that scrapped a two-term presidential limit, and another in 2016 that extended the presidential term of office to seven years from five.
Aliyev brought forward the date of the latest vote to April 11 from Oct. 17, a move his allies said was necessary to avoid presidential and parliamentary elections clashing in 2025.
Seven other candidates were running in Wednesday’s election, which will have international monitors including the Organisation for Cooperation and Security in Europe (OSCE), but critics questioned whether the other candidates were genuine.
Aliyev has tried to strike a balance between big regional power Russia, Azerbaijan’s former Soviet master, and the West, notably on energy policy.
His rule has benefited from an economic boom fueled by oil exports but a slump in global crude prices in the last three years has weakened the Azeri currency and shrunk the economy.
Many people in Azerbaijan are struggling on low incomes and amid a growing gap between rich and poor, and tensions are rising with neighboring Armenia over a territorial conflict that caused a war in the 1990s.
There are 5.2 million eligible voters in the country of 9 million people. The president is directly elected by an absolute majority of votes cast, with no turnout requirement.
Polls open at 8 a.m. (0400 GMT) and close at 7 p.m. (1500 GMT). First official preliminary results are expected within hours of the polls closing.
