He defeated four other aspirants to win the ticket by polling 3,430 votes at the party’s third national convention held at the Teslim Balogun Stadium, Lagos.
Former Vice President Atiku Abubakar scored 954 votes.
The three other were Kano Governor, Rabiu Kwankwaso; Imo Governor, Rochas Okorocha, and Publisher of Leadership Newspapers, Sam Nda-Isaiah.
With his victory, Buhari, 72, will face President Goodluck Jonathan of the Peoples Democratic Party (PDP) whose sole candidacy was ratified at the party’s special convention in Abuja earlier on Thursday.
Both men contested the presidential election in 2011.
This is Buhari’s fourth attempt having also run in 2003 against Olusegun Obasanjo and Umaru Yar’Adua in 2007.
The 2015 presidential election is scheduled for February 14.