The former diplomat, who came to power in 2019 as Nazarbayev's hand-picked successor when the country's only ruler since the Soviet era stepped down, broke with his ex-patron after a January uprising that Tokayev called a coup attempt.
A new election victory - a foregone conclusion against five little-known candidates - will give Tokayev, 69, the sort of overwhelming personal mandate that Nazarbayev routinely secured as he built a personality cult over five successive terms.
Nazarbayev, who had held on to important posts after stepping down, gave them up during the uprising in which 238 people died. Tokayev has since forced Nazarbayev allies to relinquish other positions, and changed the name of the capital - renamed "Nur-Sultan" in Nazarbayev's honour - back to Astana.
Tokayev called in Russian help to put down the unrest, but has since kept his distance from Moscow, avoiding giving public backing to Russia's war in Ukraine.
Russia is Kazakhstan's biggest trading partner, and Russia's slide into recession has hurt Kazakh economic growth, while the strength of the rouble boosted by capital controls has helped push inflation in Kazakhstan to a 14-year high.
Tokayev, a former foreign minister and deputy secretary general of the United Nations, has overseen constitutional reforms which limit his own rule to two terms. He has also promised to reduce income inequality by rooting out corruption and redistributing wealth more fairly.
He said on Sunday he would continue "resetting" the political system by calling an early parliamentary election next year. Tokayev quit the ruling Amanat party this year and oversaw reforms making it easier to establish new political parties.
Opinion polls have predicted none of the five other candidates would score in the double digits.
"Among those who are running for president, I only know Tokayev, firstly," Timerlan Sadykov, a resident of Kazakhstan's biggest city Almaty, said on the eve of the vote.
"And secondly, the way he's conducted himself on the international stage has been very appealing."
Another Almaty voter, a 35-year-old manager who only gave his first name, Serik, said he voted against all candidates.
"...I think the powers that be must realise they have given us no real choice," he said.
Almost 39% of voters cast their ballots by noon. Exit poll data will be published hours after polls close at 8 p.m. (1400 GMT) and preliminary results of the vote are expected on Monday.
(Reporting by Olzhas Auyezov and Mariya GordeyevaAdditional reporting by Tamara Vall in AstanaEditing by Peter Graff and Frances Kerry)
