He began his career in New Hampshire politics as a state representative and was elected Secretary of State in 1976 by the state legislature. He has been kept in office by both Democratic and Republican legislatures since then.
Gardner has taken the lead in New Hampshire's policy towards "100% Paper Ballot" elections, in contrast to some states that use computerized voting systems without paper records of each vote.
A strong supporter of New Hampshire's standing as the 'first in the nation' primary state, Gardner wrote Why New Hampshire with the late former Governor Hugh Gregg in October 2003, detailing the history and significance of the New Hampshire Primary. He also appears in Winning New Hampshire, released in 2004.