The Ultralightweight Field Howitzer (UFH), designated M777A1 in the USA, was selected in 1997 by a joint US Army / Marine Corps initiative to replace the existing inventory of M198 155mm towed howitzers. The first of five EMD systems was delivered in June 2000. The US Marine Corps is to procure 380 systems and the US Army 273 systems. A Low Rate Initial Production (LRIP) contract for 94 systems was awarded in November 2002.

Operational testing with the USMC, during which nearly 12,000 artillery rounds were fired by four production systems, was completed in December 2004. A contract for full-rate production of 495 systems was awarded to BAE Systems in April 2005. In May 2005, the USMC began fielding the M777 with the 11th Marines unit at Twentynine Palms in California.

The first 18 systems were delivered to the US Army's 2nd Battalion, 11th Field Artillery in Hawaii in October 2006.

The M777 will be the artillery system for the Stryker Brigade Combat Teams (SBCT). The systems will be fitted with the digital fire control system in 2007 to achieve the designation M777A1.

In December 2005, the first four of six M777 systems were supplied by the USMC to the Canadian Army, under a Foreign Military Sales (FMS) contract. The systems were deployed to Afghanistan in February 2006.

BAE Systems has developed a mobile version, the M777 Portee, which is mounted on a purpose-built 8x6 Supacat vehicle. The system is to be offered for the UK Army Lightweight Mobile Artillery Weapon System - Gun, LIMAWS(G), requirement. The vehicle was first shown at Eurosatory in June 2006.