Pro Patria Union
After the resignation of Tunne Kelam he was elected the Chairman of Pro Patria Union on 16 April 2005. In November 2005 he unveiled plans of merger between Pro Patria Union and Union for the Republic - Res Publica. After the merger of the parties on 4 June 2006 he became one of the two co-Chairmen of the new Union of Pro Patria and Res Publica. At the party congress on 26 May 2007 Mart Laar was elected a new Chairman of the Union and Tõnis Lukas became one of the three Vice-Chairmen elected to assist Mart Laar.