The president's victory over his closest challenger, Atiku Abubakar, a former vice president, means he'll extend his stay in the Presidential Villa after his first victory in 2015.
In his acceptance speech, Buhari said he'll work hard to ensure that all sections of the society are catered for under his government.
"The new Administration will intensify its efforts in Security, Restructuring the Economy and Fighting Corruption. We have laid down the foundation and we are committed to seeing matters to the end.
We will strive to strengthen our unity and inclusiveness so that no section or group will feel left behind or left out," he said.
The president also promised to further improve on the three focal points of his administration to improve the economy, secure the country and fight corruption.
He thanked the leadership of the All Progressives Congress (APC) for working hard for his victory and also expressed his gratitude to Nigerians or giving him a second chance.
Buhari won 15,191,847 of the total votes cast while Atiku gained 11,262,978 votes, an astonishing victory margin of 3,928,869 votes.
The president won in 19 states including Ekiti (219,231), Osun (347,634), Kwara (308,984), Nasarawa (289,903), Kogi (285,894), Gombe (402,961), Yobe (497,914), Niger (612,371), Jigawa (794,738), and Kaduna (993,445).
Other states where he won are Bauchi (798,428), Lagos (580,825), Ogun (281,762), Kano (1,464,768), Katsina (1,232,133), Borno (836,496), Sokoto (490,333), Kebbi (581,552), and Zamfara (438,682).
Atiku won in 18 states including the FCT (259,997), Ondo (275,901), Abia (219,698), Enugu (355,553), Ebonyi (258,573), Anambra (524,738), Oyo (366,690), Adamawa (410,266), Edo (275,691), Benue (275,691).
Other states where he won are Imo (334,923), Plateau (548,665), Taraba (374,743), Cross River (295,737), Akwa-Ibom (395,832), Delta (594,068), Bayelsa (197,933) and Rivers (473,971).
Buhari won his first term victory in 2015 after he beat then-incumbent, Goodluck Jonathan, by 2,571,759 votes as he won 15,424,921 votes over his opponent's 12,853,162 votes.
Atiku has not yet called President Buhari to concede defeat like Jonathan did when he was defeated by the former military Head of State in 2015.