From 1996 till 2010, McAllister was a member of the Cuxhaven district council (Kreistag). He served as mayor of his hometown of Bad Bederkesa from 2001 to 2002. From 2002 to 2003, he also was secretary general of the CDU in Lower Saxony. Since 2003, McAllister has been the leader of the CDU parliamentary party group in the Parliament of Lower Saxony, of which he has been a member since 1998. McAllister succeeded Christian Wulff as party chairman of the CDU in Lower Saxony in June 2008, winning the election by a record margin. In 2016, he was succeeded by Bernd Althusmann. In the United Kingdom, McAllister is a supporter of the Conservative Party.