He was chief executive of the New Zealand Make-a-Wish Foundation from 2008 to 2011,[2] and previously a member of the National Party board of directors.

He previously stood for selection as the National Party candidate for Tamaki in 2004, but lost to Allan Peachey.

[11] During the 2014 New Zealand general election, Simpson was re-elected in Coromandel by a margin of 15,801, defeating the Green Party's candidate Catherine Delahunty.

[11][13] During the 2017 New Zealand general election, Simpson was re-elected in Coromandel by a margin of 14,326 votes over Labour's Nathaniel James Blomfield.

[11] During the 2020 New Zealand general election, Simpson retained Coromandel for a fourth term by a final margin of 3,505 votes over Labour's Nathaniel James Blomfield.

[15] During the 2023 New Zealand general election, Simpson retained Coromandel for a fifth term by a margin of 17,349 votes over Labour's Beryl Riley.