Former chief minister and Punjab Lok Congress chief Amarinder Singh joined the Bharatiya Janata Party in New Delhi on Monday in the presence of senior BJP leaders Narinder Singh Tomar and Kiren Rijiju.
Singh also merged his newly formed Punjab Lok Congress (PLC) with the BJP.
Singh, 80, had floated the PLC last year after quitting the Congress following his unceremonious exit as chief minister, but his party failed to win any seat in the state assembly polls.
Singh himself lost from his home turf of Patiala Urban.
The PLC contested the elections in alliance with the BJP and the Sukhdev Singh Dhindsa-led Shiromani Akali Dal (Sanyukt).
Along with Singh, former deputy speaker of Punjab Assembly Ajaib Singh Bhatti also joined the BJP.
Singh, the two-time former chief minister, is the scion of the erstwhile Patiala royal family.
Before his joining, Singh met BJP president J P Nadda.