He was a member of the House of Commons of Canada from 2003 to 2015, and represented the riding of Perth Wellington for the Conservative Party.
A councillor in the former Downie Township, Ontario from 1988 to 2000, he first ran for parliament in the 1997 federal election as a Progressive Conservative in Perth—Middlesex.
The subsequent by-election in 2003 garnered national attention, as both the Progressive Conservative and Canadian Alliance candidates attempted to displace the governing Liberals in the riding.
Schellenberger, still running as a Progressive Conservative, defeated Liberal Brian Innes by 1,001 votes; despite several appearances from party leader Stephen Harper, the Alliance candidate, Marian Meinen, finished a distant third.
Shortly after his election, Schellenberger endorsed Peter MacKay for the leadership of the Progressive Conservative Party.
In the 2006 federal election, Schellenberger was re-elected by a margin of 9,703 votes, defeating the Liberal candidate, David Cunningham.