The system, which entered full-production in 2005, is the world's first artillery weapon to make widespread use of titanium and aluminum alloys.
The weapon weights less than 9,300 pounds -- about half the weight of conventional 155mm systems.
The company said the 1,000 unit mark was surpassed by a recent order for 46 howitzers by the U.S. Defense Department.
"M777's capability is proven in combat daily -- being sling-loaded under helicopters and air-dropped in some of the most demanding operational conditions on the planet," said Mike Smith, managing director of BAE Systems' Global Combat Systems Weapons business. "These additional orders serve to reinforce the confidence that our customers have in the system and its support.
"The M777 has passed every development and operational test in vital areas such as accuracy, consistency, operational flexibility and mobility. There is no other modern howitzer which has been subjected to such rigorous examination or been engaged in such unrelenting operational usage and regular deployment by airborne assets."
BAE Systems' facility at Hattiesburg, Miss., is responsible for final integration and test of the weapon system. The prime contract management of the M777 program and manufacture and assembly of the complex titanium structures and associated recoil components are undertaken at Barrow-in-Furness, England.
The M777 effort is managed by the U.S. Army/Marines Light Weight 155mm Joint Program Office at Picatinny Arsenal in New Jersey.