Although an engineer himself, with an industrial background in coal and steel, Mouchel was first and foremost a businessman. He established LG Mouchel in 1897 as an engineering consultancy, initially specialising in ferro-concrete. The business was immediately fruitful — Mouchel's first contract was to design retaining bank piles for a new sea wall in Southampton for the London & South Western Railway. The demand for ferro-concrete proved to be high. By the early 20th century it had become an aspirational and revolutionary material, representing modernity, strength and versatility.

Mouchel was an anglophile with a passion for the British way of life, spending the majority of his adulthood living and working in the UK. Although he never lost his broad Normandy accent, he spoke and wrote English with perfect accuracy. In spite of his dedication to the British way of life, Mouchel was always aware that, to those around him, he was considered a Frenchman. An acquaintance of his once remarked, "But, you see, you are not an Englishman". "No", replied Mouchel, "but I am nearly as bad. I am a Norman."

Today the company that Louis Gustave Mouchel founded in his own name — L.G. Mouchel & Partners, now known as simply Mouchel — is one of the largest technical consultants in the UK, and is a publically listed company.