Without any opinion polls, it is not clear whether any candidate will secure over 50% of the vote to prevent a runoff.
'Diomaye is Sonko'
Macky Sall, first elected in 2012, is leaving on a drop in popularity that worsened when he unsuccessfully sought to postpone the vote - initially scheduled on February 25 - to December.
The move stoked unrest and concerns about authoritarian overreach in the nation of around 18 million. It also buoyed opposition parties that rejected all attempts to delay the vote which could have extended the president's mandate.
Senegal's Constitutional Council sided with opposition parties, ruling that the vote should go ahead and that Sall's mandate could not be extended beyond April 2.
An amnesty law passed to ease tensions this month meanwhile allowed Sonko, and Faye - who had also been in detention for nearly a year, on charges including defamation and contempt of court -- to be released.
Both have hit the campaign trail under the banner "Diomaye is Sonko" as a crowd-pleasing duo.
Sonko, who came third in the last election in 2019, is particularly popular among urban youth frustrated with lack of jobs and high living costs in a country where 60% of the population is younger than 25.
"The election will show whether their popularity on social media is real," said Senegalese political analyst Babacar Ndiaye.
Most of Sonko's supporters are now expected to vote for Faye, analysts say. He has promised to root out allegedly entrenched corruption, restore stability and prioritize economic sovereignty.
But some of Faye's campaign promises, such as plans to renegotiate oil contracts just as Senegal is due to begin offshore oil and gas production, and the introduction of a national currency, have raised concerns that these could hurt the country's image as a destination for investors.