Result of the vote, held less than one year before presidential election, is in stark contrast to last year's parliamentary elections when the Democratic Party enjoyed a sweeping victory that gave it a super-majority in the National Assembly.
Ruling party candidate Mohamed Bazoum is seen by many as the favourite after leading in the first round on December 27 with 39.3 percent of the vote. Polling stations opened at 0700 GMT and will close at 1800 GMT (8 am to 7pm) local time.
Senate leaders have agreed to rules of impeachment for the trial, including a debate and vote on whether it’s even constitutional to prosecute former president Trump but the outcome is likely to stop proceedings with Democrats in majority.