In the 53rd Parliament, Matt was promoted to National's Senior Whip and Spokesperson for Mental Health, Associate Spokesperson for Health and Associate Spokesperson for Social Development and Employment. In National leader Christopher Luxon's caucus, Matt was promoted to the front bench to number eight in the caucus, where he holds the portfolios of Mental Health, Youth, Associate Health and Associate Transport.

In the 52nd Parliament, Matt served as National’s Junior Whip, Spokesperson for Mental Health, Associate Spokesperson for Health and was a member of the Health Select Committee.

As National’s first ever Spokesperson for Mental Health, in 2018 Matt wrote to every political party in Parliament to invite them to join a cross-party approach to mental health that would focus on developing solutions and policy over a longer period than the Parliamentary three-year term. Matt believed that by initiating a bipartisan approach to mental health, this would break down some of the barriers to progress to improve mental-health outcomes in New Zealand. On 28 August 2019, Sir John Kirwan launched the Mental Health and Addictions Wellbeing cross-party group, with the executive consisting of Matt Doocey, Louisa Wall (Labour), Chloe Swarbrick (Green Party), Jenny Marcroft (NZ First) and David Seymour (ACT), to work together to improve mental health and wellbeing in New Zealand.