Kishor had shot to fame in 2014 when he managed the poll campaign for Narendra Modi.
Election campaign strategist Prashant Kishor joined Bihar Chief Minister Nitish Kumar's Janata Dal (United) on September 16.
Kishor was inducted into the party by Kumar, who is also the national president of the JD(U), at the organisation's state executive meeting which is underway at the chief minister's official residence, sources said.
Kumar welcomed the 41-year-old into the party by presenting him with an "angavastram" (stole) and the poll strategist was given a seat next to the chief minister at the state executive meet, they said.
It was not immediately known what role he has been assigned to in the party wherein he has been inducted barely a few months ahead of the Lok Sabha polls.
Earlier, Kishor had tweeted "excited to start my new journey from Bihar".
A resident of Buxar district in the state, Kishor had shot to fame in 2014 when he managed the poll campaign for Narendra Modi, then the prime ministerial candidate of the BJP, which went on to put up its best-ever electoral performance.
A year later, he collaborated with Kumar who returned to power for his third consecutive term after registering a handsome victory in the assembly polls which the JD(U) had fought in alliance with the RJD and the Congress.
The chief minister rewarded Kishor by appointing him as his adviser and giving him a cabinet minister rank.Kishor thereafter worked with the Congress in Punjab where the party returned to power dislodging the Shiromani Akali Dal (SAD)-BJP combine which had been ruling the state for a decade.