After a short stint working as a researcher for the Department of Criminology, University of Cambridge, he qualified as a lawyer with the London firm then known as Denton, Hall and Burgin.
In 1979/1980, Sinclair attended Columbia University School of Law in New York and obtained a LAM in International Legal Studies, and qualified for the State Bar of California.
In 2014, Sinclair founded documentary, television and film company White Horse Pictures alongside East with partners Nicholas Ferrall, Cassidy Hartmann and Jeanne Elfant Festa.
[2] With White Horse Pictures, Sinclair has produced a series acclaimed documentaries, including Ron Howard's The Beatles: Eight Days A Week - The Touring Years and Pavarotti, The Apollo (exec) directed by Roger Ross Williams, The Bee Gees: How Can You Mend a Broken Heart directed by Frank Marshall, and Amy Poehler's documentary directorial debut Lucy and Desi.
In addition, Sinclair was executive producer on Ron Howard's epic action-thriller Rush, set in the spectacular world of Formula 1 auto racing.
At White Horse, Sinclair's latest productions include a feature adaptation of Conn Iggulden's Emperor series about Julius Caesar's early years and a biopic about The Who drummer Keith Moon.
Sinclair also served as an executive producer on the Hammer Films production and box-office hit The Woman in Black, starring Daniel Radcliffe.