58-year-old had undergone months of medical treatment in Saudi Arabia before returning home in February.
President Umaru Yar'Adua, who returned to Nigeria in February after months of medical treatment in Saudi Arabia, has died at the age of 58.
A presidential spokesman told the Associated Press that Yar'Adua died at 9pm yesterday at the Aso Rock presidential villa.
Yar'Adua had not been seen in public since he returned from the Middle East. He went for medical treatment at a clinic in Jeddah for pericarditis, an inflammation of the membrane surrounding the heart.
Rumours swirled about his health, and his prolonged absence led to protests about the lack of clear lines of authority in a country of 150 million people.
Just before Yar'Adua returned to Nigeria, parliament voted to transfer power to Goodluck Jonathan, the vice-president, until the president was fit to resume his duties. At the time, many Nigerians doubted that Yar'Adua would ever be well enough, casting a question mark over the leadership of the ruling party in the runup to next year's presidential election.
Yar'Adua, who has also suffered kidney problems, left the country several times for what his advisers called medical checkups before he went to Saudi Arabia in November. He was admitted to a hospital the day after he arrived, leaving Nigeria in a political vacuum.
Last month, Jonathan sacked all cabinet ministers in an attempt to stamp his authority on Africa's most populous country. He dissolved the cabinet without explanation in his first major act since assuming executive powers. The move in effect left the quiet 52-year-old biologist in sole command of government.
The cabinet had consisted mainly of ministers loyal to the ailing president, a Muslim, although some members had begun to shift allegiance to Jonathan, a Christian from the south.