Thapar, who was the PPP general secretary, said that he was leaving the party as it had never followed the ideology of martyrs and alleged that its president, Manpreet Singh Badal, had misled martyrs' families for narrow political interests.
Thapar joined the ruling SAD in the presence of party president and Deputy Chief Minister Sukhbir Singh Badal, a release said.
Harjiwanpal Singh Gill, another general secretary of the PPP and party secretary and spokesman Arunjot Singh Sodhi, too switched to the SAD, the release added.