Adityanath has been a vocal and firebrand Hindutva leader who courted controversy recently after video footage showed him daring people behind what the party calls 'Love Jihad'. He allegedly threatened to convert 100 Muslim girls to Hindusim for each Hindu converted to Islam.
The 42-year-old MP was recently locked in a battle of words with Samajwadi Party (SP) chief Mulayam Singh Yadav in the Lok Sabha during a debate.
He has often accused the SP and the Congress of appeasing the Muslim community for electoral gains.
He is one of the three star campaigners for the 11 state assembly and one parliamentary seat which go to by-polls Sep 13.
The other two campaigners named by the BJP's central election committee are Union Minister Kalraj Mishra and state president Laxmikant Bajpayi.
The opposition parties allege that Adityanath's appointment was yet another indication that the BJP was trying to polarise the by-polls on religious lines.