[1] Diehl was the unsuccessful Republican nominee for the U.S. Senate in 2018 and for governor of Massachusetts in 2022, losing both elections in landslides to Democrats Elizabeth Warren and Maura Healey respectively.

He attended Lake Forest Academy and graduated from Lehigh University in 1992 with a Bachelor of Arts degree in Government and Urban Studies (double major).

Diehl received support from previous representatives from the same district, including Andrew Card, Michael Sullivan, Ned Kirby, and Ronald Whitney.

He was a member of the Joint Committee on Ways & Means, Housing, Transportation, Global Warming and Climate Change, Personnel & Administration, and Rules.

Geoff Diehl was a lead supporter of the successful ballot question campaign to repeal the Massachusetts gas tax indexing law in 2014.

[12] As a candidate, Diehl criticized federal and state mandates[13] put in place during the COVID-19 pandemic and continuously supported workers and first responders being fired for not taking the vaccine.