Polling stations closed on Sunday, with official results expected within the next two weeks.
The election was marked by low turnout, as many voters expressed doubts that the vote would lead to political change after more than forty years of leadership by the 82-year-old incumbent.
Several opposition parties had also called for a boycott of the polls.
Six other candidates contested the presidency in the oil-rich Central African nation, but analysts say none poses a serious challenge to Sassou N’Guesso, who is running under the banner of the Congolese Party of Labor.
Sassou N’Guesso first took power in 1979 and ruled until 1992 before returning to office after the Second Republic of the Congo Civil War (1997).
A 2015 constitutional referendum removed presidential age and term limits, allowing him to run again.
The election comes as the Republic of the Congo faces economic pressures, including rising debt and youth unemployment.
If confirmed, Sassou N’Guesso’s victory would place him among Africa’s longest-serving leaders, alongside Paul Biya of Cameroon and Teodoro Obiang Nguema Mbasogo of Equatorial Guinea.
