After graduating from ENSAD (École Nationale Supérieure des Arts Décoratifs) in Paris, Sadler soon began to specialize in plastics, contributing to the innovation of manufacturing technologies. Sadler gained fame as a designer of technical sports accessories in the 1970s when he designed and patented a thermoplastic ski boot with a symmetrical shell that met with great success. His collaboration with sports companies was fundamental for his career. In addition to his long-standing relationship with the Italian company Caber, which later became Lotto, in the 1990s, he designed an innovative back protector for the Dainese motorbike brand, which is now part of MoMA's permanent design collection.

Sadler won the ADI Compasso d'Oro several times - in 1994 for the Drop rubber wall lamp for Flos; in 2001 for the Tite and Mite lamps for Foscarini (the latter included in the permanent design collection of the Beaubourg in Paris), made with a mix of carbon wire and fiberglass, which together allow for a functional structure and a characteristic graphic decoration; in 2008 for the Big bookcase for Caimi Brevetti, with aluminium uprights and painted steel shelves; in 2014 for the Bellevue refrigerated counter with Panorama technology for IFI, which makes it possible to use the traditional ice cream well structure for both storage and visibility. He recently designed the Tyla floor lamp for Kundalini (2021), inspired by the shape of an aquatic plant. He won the 2020 Archiproducts Design Award with the Accordéon lamp for Slamp.

Throughout his career, Sadler has worked on furniture, lighting, small and large household appliances, always favoring plastic materials and often experimenting with innovative production processes. He has collaborated with the Tim telephone company and the Ferragamo fashion house for the design of anti-shop fitting systems, window dressing and display modules.