Sinclair worked as director of the Jolie-Pitt Foundation from November 2013 to December 2015 including overseeing construction of a children's hospital in Ethiopia.

[5] Projects included emergency short term housing for those displaced by man-made and natural disasters; livelihoods for vulnerable communities; Community-led adventure travel and rural revitalization.

Sinclair partnered with MADE Collective to propose the world's first co-nation called Otra Nation[6] and BorderBNB, a home-share platform for families separated by political conflict and natural disasters.

Having developed an interest in social, cultural and humanitarian design, his postgraduate thesis focused on providing shelter to New York's homeless through sustainable, transitional housing.

Architecture for Humanity was co-founded by Sinclair in 1999 and grew to include 90,000 design professionals, 5 regional offices around the globe and 70 independent city-based chapters.

The organization worked in forty eight countries on projects ranging from school, health clinics, affordable housing and long-term sustainable reconstruction.

Sinclair is a regular lecturer and visiting professor and has spoken at a number of international conferences on sustainable development and post disaster reconstruction.

From November 2013 to December 2015, Sinclair worked for a private family foundation on health, education, conservation projects in Cambodia, Ethiopia and Namibia.

In 2016 Sinclair joined Airbnb to lead social innovation and supported the humanitarian efforts at the company with a goal to create temporary housing for 100,000 people over the next 5 years.