President Abdoulaye Wade faces a challenge from his former political ally Macky Sall in the vote.
Wade’s controversial bid for a third term triggered street protests in the normally calm West African state ahead of the February 26 first round, and galvanised the opposition against him.
Wade, 85, took 34.8 percent of the first-round votes, ahead of Sall’s 26.6 percent but short of the outright majority he had predicted and needed to avoid a run-off.
“The second round of the presidential election will be held Sunday, March 25, 2012,” Mariama Diop, a constitutional council official, told a news conference.
Sall, a former prime minister in Wade’s government, has called on other opposition parties to back him in the second round and has won the support of hugely popular Senegalese musician Youssou N’Dour.
Wade has been in power since 2000 and has argued his first term should not count toward a two-term limit adopted in 2001. Reuters