MONROVIA, Liberia — Ellen Johnson Sirleaf, the first woman democratically elected as a head of state in Africa, was awarded the $5 million Ibrahim Prize for Achievement in African Leadership on Monday for “transformative leadership” in the aftermath of Liberia’s civil war.

Ms. Johnson Sirleaf governed Liberia, a small West African nation that was founded by freed slaves from the United States, for 12 years. When she left office last month and turned over power to George Weah, a former soccer star, it was the country’s first peaceful, democratic transition of power in 73 years.

“She took over a country that was devastated and broken by 14 years of civil war, and was later struck again by the Ebola crisis,” the prize citation said, while adding: “Such a journey cannot be without some shortcomings. Today, Liberia continues to face many challenges.”

Established in 2006, the Ibrahim Prize goes to democratically African leaders who have left office after their “constitutionally mandated term.” Ms. Johnson Sirleaf is the first woman to be awarded the prize.