Alongside the now-defunct Crown Coach, the company was one of the largest manufacturers of school buses on the West Coast of the United States.

[4] Following the earthquake, the company reopened as the Leo Gillig Automobile Works, which manufactured custom-built vehicle bodies.

While other hardtop manufacturers went out of business, Gillig survived largely on its body production, which became its primary source of revenue.

[4] Following the start of the Great Depression, Gillig Brothers began to look for a steady source of revenue to ensure its survival.

The first mid-engine school bus, the Transit Coach wore an all-steel body and was powered by a Hall-Scott gasoline engine.

[4] During World War II, Gillig halted school bus production, instead producing trailer buses to transport workers in defense factories.

The management structure of the family-run company was changed, with Stanley Marx (previously in charge of sales),[4] assuming control of Gillig.

In 1957, a major acquisition was made as Gillig purchased the Pacific bus division of Washington-based truck manufacturer Kenworth.

Although still offered with gasoline engines in various configurations, the C-Series Transit Coach accounted for over three-quarter of all Gillig sales within only five years.

[4] During the acquisition and reorganization, Gillig began construction on a 117,000 square foot facility in Hayward, the largest bus manufacturing plant in the western United States.

Following the end of the "New Look" near-monopoly of GMC and Flxible, in mid-1976, Gillig entered a partnership with West German manufacturer Neoplan to build a series of European-styled transit buses.

During the 2000s, Gillig would make a number of advances with its vehicles, exploring the uses of alternative fuels and hybrid technologies in both the Low Floor and the Phantom.

After 28 years of production, the final Gillig Phantom was produced in 2008; by the mid-2000s, high-floor buses had largely fallen out of favor with transit customers.

[12] In 1992, Gillig began producing an LNG fueled version of the Phantom as a lower emissions option, but discontinued it in 1998.

In September 2011, Gillig introduced an alternative fuel BRT model with CNG propulsion—their first CNG-powered bus produced and first production natural gas buses since 1998.

[15] The bus uses the Gillig Low Floor platform and is equipped with a traction motor with a peak power and torque of 350 kW (470 hp; 480 PS) and 3,500 N⋅m (2,600 lb⋅ft);[16] it is expected to have a range of approximately 150 mi (240 km), based on battery capacity (444 kW-hr) and consumption (2.3 kW-hr/mi).

Meanwhile, the Seattle transit agency removed the propulsion system (GE traction motor, Randtronics chopper control, and electronic card cage) from its old fleet of 1979-built AM General trolley coaches[19] which the Gillig vehicles were purchased to replace, and shipped them to Alstom for refurbishment.

[20] After Alstom refurbished the propulsion system, Metro installed the equipment into the new Gillig Phantom bodies, along with Kiepe pneumatically operated fiberglass trolley poles.