The longtime ruler inked the document two months after it was overwhelmingly approved in a referendum.
"This day is an historic day, it's about the future," Constitutional Affairs Minister Eric Matinenga said at the signing ceremony, held in a marquee erected on the lush green lawns of the State House.
"I can assure you that this document which is before us is a good document."
A new Constitution is one of the pre-conditions for elections to pick a successor to the shaky compromise government Mugabe formed four years ago with his nemesis Prime Minister Morgan Tsvangirai.
Limited presidential tenures
The new Constitution curtails the president's powers, limits presidential tenures to two five-year terms and does away with the post of prime minister.
Mugabe (89) has ruled Zimbabwe since the country gained independence from Britain in 1980.
His 33-year-rule has been tainted by allegations of rights abuses against his opponents and critics.
The constitution was endorsed in a referendum in March and later sailed unopposed through both houses of parliament.
Mugabe and Tsvangirai formed a power-sharing government four years ago to avoid a descent into full-scale conflict in the aftermath of a bloody presidential run-off election in 2008.
The power-sharing government has been hobbled by frequent haggling over the allocations of key government posts, the implementation of key reforms and charges of violence.
Elections should be held this year but the date is yet to be set.
Mugabe and his allies want the polls as soon as possible while Tsvangirai insists on the application of reforms first to ensure a free and fair vote. – AFP