[1] He was previously a professor at the University of Auckland and was the first director of Te Pūnaha Matatini, a centre of research excellence in complex systems and data analytics.

[2] During the COVID-19 pandemic in New Zealand, he led a team of scientists developing mathematical models of the spread of the virus across the country that influenced the government's response to the outbreak.

[6] After completing his PhD, Hendy went to work at Industrial Research Limited in Lower Hutt on a New Zealand Science and Technology post-doctoral fellowship.

[9] Hendy was motivated to study the science of complex systems after hearing about the work of physicist Geoffrey West on the link between population distributions and innovation.

Te Pūnaha Matatini develops tools to analyse data from a range of social, economic and biological systems, to inform and evaluate government policy and decision-making.

[29][30] He expressed concern about New Zealand's Anzac Day long weekend (25–27 April) encouraging a rise in social activity if the lockdown were eased before then, potentially spreading the virus further.

[31] In late December 2021, Hendy and epidemiologist Siouxsie Wiles filed a complaint with the Employment Relations Authority against the University of Auckland for allegedly not protecting them from abuse by anti-lockdown and anti-vaccination elements.

The University of Auckland had responded by issuing a written statement in August 2021 advising them to minimise their public commentary and social media interaction; which Hendy and Wiles regarded as insufficient.