In 1813, he moved to London, first working for Alexander Galloway in Holborn. He soon left in search of wages more suiting his skills, moving to Joseph Bramah at Pimlico. Bramah doubled the wages Galloway had paid and entered into a formal agreement with Clement for a term of five years, dated 1 April 1814, making him chief draughtsman and superintendent of Bramah's Pimlico works. Following Bramah's death, Clement took up a position as chief draughtsman at Maudslay, Sons and Field, in Lambeth, where he played a role in the design of the firm's early marine steam engines. In 1817 he left Maudslay and Field to set up his own firm, encouraged by the Duke of Northumberland, a frequent visitor to Maudslay's works. Clement had managed to save the sum of £500 and took a small workshop at 21 Prospect Place, Newington, where he set up in business as a draughtsman and manufacturer of precision machinery. In 1818 he was awarded the gold medal of the Society for the Encouragement of Arts for his invention of a machine for marking ellipses, inspired by the trammels used by carpenters. Clement's main interest was the improvement of self-acting machine tools, and especially lathes. He introduced various improvements in the construction of lathes, being awarded the gold Isis medal of the Society for the Encouragement of Arts in 1827 for his improved lathe which was of unprecedented precision and accuracy. The next year he added his self-adjusting centre chuck to the lathe, for which the Society of Arts awarded him their silver medal. The same year, Clement began making fluted screw-cutting tap and dies and urged the adoption of a standard system of screw threads where every machine screw of a particular length should have a set number of threads of a predetermined pitch and determined the number of threads for each length. Joseph Whitworth, at that time one of Clement's journeymen afterwards played a major role in such standardisation, the Whitworth thread becoming a standard for machine screws. Regarding Clement's building of planers, Roe says,
The recognised excellence of Clement's machine tools and his skill in precision engineering led to him being employed by Charles Babbage in 1823 to work on his project to design and build his mechanical calculating device, the difference engine. The high prices of his large precision tools led to a falling out with Babbage, but his skill and the quality of his products kept him in employment for many years.
Later years
In later years, Clement returned to music and constructed an organ. He died on 28 February 1844 at 31 St George's Road, Southwark. Although he had never married, he had a daughter, Sarah Clement, by one Agnes Esson from County Durham.