Kibaki's death was announced by President Uhuru Kenyatta, who said his passing was a sad day for the country and praised his predecessor as a great Kenyan and a statesman.
Former Kenyan President Mwai Kibaki, who led the East African nation for more than a decade, has died, his successor Uhuru Kenyatta has announced. He was 90.
"It is a sad day for us as a country. We have lost a great leader," Kenyatta said in an address on state television on Friday.
Kenyan politicians, African leaders and former colonial ruler Britain were among those to send their condolences.
Details about his death have not been officially disclosed. However his health had fluctuated since a serious car accident in 2002 and he had been in and out of hospital in recent years.
Kenyatta said a state funeral would be held, without giving a date.
He also ordered a period of national mourning from Friday until sunset on the day he is buried, with all flags on public buildings to be flown at half-mast.
"President Kibaki will be forever remembered as the gentleman of Kenyan politics, a brilliant debater whose eloquence, wit, and charm won the day time-and-time again."
Kibaki, a veteran politician whose career dated back to the birth of independent Kenya, served as the country's third president from December 2002 to April 2013, taking over from the authoritarian rule of Daniel arap Moi.
His rule saw the most violent election in Kenya's history when more than 1,100 people died in bloody ethnic battles after disputed 2007 polls, but he also oversaw the adoption of a new constitution with reforms aimed at preventing such unrest.
Kibaki left a legacy of strong growth in the regional economic powerhouse, launching major infrastructure projects and boosting the struggling health and education sectors.
But his rule was also marred by rampant government corruption and his lavish spending on flagship projects contributed to the country's debt mountain.
Tributes came from across Kenya and the African continent, from Burundi to Zambia, as well as regional blocs.
"The region shares in your loss of an iconic leader & visionary statesman," Workneh Gebeyehu, executive secretary of the Intergovernmental Authority on Development (IGAD), said on Twitter.
"Kibaki is one of the freedom fighters of our country, he served this country for many years with diligence, forthrightness, honesty and transparency," said veteran Kenyan leader Raila Odinga, who is making his fifth run for the presidency in August elections.