The first Australian-built Sigmas were released in October 1977 to replace the outgoing GD series Galant and were badged as Chryslers. The GE series Sigma was the first to introduce the Australian market to the Astron engine range; the 1.6-litre Saturn engine was also available in the base model Sigma Galant. The mid-range model was the Sigma GL and came standard with the Astron (1.85- or 2.0-litre) and four-speed manual. The top-line model was the Sigma SE and was initially only available with the Astron 2000 with three-speed automatic. It had equipment levels never seen before at the time including reclining rear seats.
In March 1978 an imported two-door coupe version called the "Sigma Scorpion" was released based on the Mitsubishi Galant Lambda, and six months later a station wagon variant was added across the whole range.
A five-speed manual was offered as standard only on the SE from 1979 and in January 1980 the 2.6-litre Astron was released and was available as an option in GL and SE trim. The 2.6 was noted to be the most smoothest and most powerful Australian-built four-cylinder engine in its day and being renowned for its low-end torque, producing 73 kilowatts (98 hp) at 4,800 rpm and 188 N·m (139 lb·ft) at 2,400 rpm. Offering performance closer to that of larger six-cylinder cars, contemporary comparisons of the 2.6 against other four-cylinder cars showed that it could outpace its locally built four-cylinder competitors.