Solvay was born at Rebecq-Rognon in Belgium. As the son of a salt refiner and the nephew of a manager of a gas plant, he was introduced at an early age to the techniques and problems of the chemical industry. He devised several methods for purifying gases but is best known for the ammonia–soda process named for him.

For most of the 19th century soda was produced by the Leblanc process. This had a number of disadvantages: it produced toxic hydrochloric acid fumes and also a number of expensive and irrecoverable waste products. As early as 1811 Augustin Fresnel had proposed an ammonia–soda process. However, although chemists succeeded in the laboratory, when they tried to translate their results onto an industrial scale they invariably ended up like James Muspratt, who lost £8000 in the period 1840–42. Solvay was the first to solve the engineering problems of the process. He later confessed that he was completely ignorant of all these earlier failures, adding that he would probably never have tried if he had known.

In 1861 Solvay took out his first patent for soda production and in 1863 set up his first factory at Charleroi, in partnership with his brother. The process involved mixing brine with ammonium carbonate, which produced sodium carbonate and ammonium chloride. The sodium carbonate yielded soda on being heated and the ammonium chloride, when mixed with carbon, regenerated the ammonium carbonate the process started from. Solvay's innovation was to introduce pressurized carbonating towers.

The system was soon adopted throughout the world and by 1900 95% of a greatly increased world production of soda came from the Solvay process. The price of soda fell by more than a half in the last quarter of the 19th century.

Solvay is also remembered for financing the great series of international conferences of physicists starting in 1911, in which much of the new nuclear and quantum physics was discussed.