Having dominated politics in the former Yugoslav republic for nearly 25 years, Djukanovic stepped down as prime minister in October 2016. He announced his comeback bid last month.
The 56-year-old economist wants to take the predominantly Orthodox country, a part of which has strong pro-Russia sympathies, into the European Union following its admission to NATO in 2017.
If he wins the presidency, currently a ceremonial post, it is expected to become the real seat of power in the country of 620,000 people.
The issue of organised crime has cast a shadow on the campaign, with some 20 people killed by assassinations in the street or car bombs over the last two years.
Polls opened at 7am (0500 GMT) and will close at 8pm, with first results shortly afterwards.
Djukanovic is the most high-profile of all the seven candidates with posters plastered all over the capital Podgorica — where a third of Montenegro’s population lives — proclaiming him as “leader, statesman and president of all citizens”.
Opinion polls predict a first-round victory. But if the veteran leader is forced into a run-off, it will be held on April 29.
– ‘Creator of chaos’ –
The opposition accuses Djukanovic of being linked to the mafia, which he denies.
“As president, I will do everything in my power… to give the police the authority that would allow them to protect citizens from those who put their lives in danger,” Djukanovic said during the campaign.
Djukanovic’s strongest rival is Mladen Bojanic, who has the support of most opposition parties, including pro-Russian factions.
Bojanic said Djukanovic “cannot be the solution because he is the creator of the instability and chaos that we witness in the streets of Montenegro.” Bojanic is expected to secure a third of the vote.
“I agree with Djukanovic that the state is stronger than mafia. But the problem is that I do not know which side he is on.”
– ‘Normal relations with Russia’ –
Another candidate, pro-Russian Marko Milacic, accuses Djukanovic of being most responsible for the “situation in the country, from bloody streets to the foreign policy and a ruined economy”.
With Montenegro’s average salary at around 500 euros ($615) and unemployment at over 20 percent, the debate over the West versus Russia is not the main concern of many Montenegrins.
For Djukanovic, however, the choice between Brussels and Moscow is crucial to whether Montenegro will “remain on its road of development”.
But he has toned down the anti-Russian rhetoric saying he wanted “normal relations with Russia if it is prepared to do the same”.
Along with Serbia, Montenegro is the favourite to join the EU next, possibly as early as 2025.
The EU in its 2016 country progress report told Montenegro it should continue its efforts to reduce organised crime, in particular on human trafficking and money laundering, and also noted the problem of international cigarette smuggling through the port of Bar.
All candidate countries are strongly encouraged to align their foreign policy with the EU, including regarding Russia.
Local newspapers have in the run-up to the vote alleged electoral fraud saying many dead people figured on voters’ lists.