Namibia's President Hage Geingob died early Sunday in a hospital in Windhoek, the presidential office said in a statement.
Geingob, 82, who was serving his second term as president, revealed last month that he was receiving treatment for cancer.
"It is with utmost sadness and regret that I inform you that our beloved Dr. Hage G. Geingob, the President of the Republic of Namibia has passed on today", read the statement on X, formerly Twitter, signed by acting president Nangolo Mbumba.
"At his side, was his dear wife Madame Monica Geingos and his children."
A biopsy following a routine medical check-up in January had revealed "cancerous cells", Geingob's office said at the time.
First elected president in 2014, Hage Geingob was Namibia's longest serving prime minister and third president.
In 2013, Geingob underwent brain surgery, and last year he underwent an aortic operation in neighbouring South Africa.
Up until his death, he had been receiving treatment at Lady Pohamba Hospital in Windhoek.
"The Namibian nation has lost a distinguished servant of the people, a liberation struggle icon, the chief architect of our constitution and the pillar of the Namibian house," said Mbumba.
"At this moment of deepest sorrow, I appeal to the nation to remain calm and collected while the Government attends to all necessary state arrangements, preparations and other protocols."
He said the Cabinet would convene immediately to make the necessary state arrangements.
Born in a village in northern Namibia in 1941, Geingob was the southern African country's first president outside of the Ovambo ethnic group, which makes up more than half the country's population.
He took up activism against South Africa's apartheid regime, which at the time ruled over Namibia, from his early schooling years before being driven into exile.
He spent almost three decades in Botswana and the United States, leaving the former for the latter in 1964.
Namibia is to hold presidential and national assembly elections towards the end of the year.
