Making the announcement, party leader and Environment Minister Prakash Javadekar said the BJP, which has just suffered a major setback in the Bihar polls, and earlier in Delhi, was confident of winning Assam.
Meanwhile, the new appointment for Sonowal -- who is union minister for youth affairs and sports -- has fuelled speculation of a cabinet reshuffle, which has long been expected in Prime Minister Narendra Modi's cabinet.
The BJP, however, made no official comment on it.
Former Congress heavyweight Himanta Biswa Sarma, who joined the BJP in August, was made convener of the election management committee, which has Sonowal as the chairman.
Sonowal -- the Lok Sabha member from Assam's Lakhimpur constituency -- replaces Siddarth Bhattacharya, who will now be a national spokesperson of the BJP on issues related to the northeast.
"We could not win in Delhi and Bihar in 2015, there are different reasons. From 2016, we will be on the victory track again and it will begin from Assam. Assam is ready for change," Javadekar said after making the announcement.
He also said BJP president Amit Shah will go to Dibrugarh on November 27 to attend a party meeting.
The BJP had appeared invincible after its massive victory in the 2014 general elections, followed by victories in Maharashtra, Haryana, Jharkhand and a coalition government in Jammu and Kashmir in the same year.
In 2015, the BJP lost Delhi to the Aam Aadmi Party (AAP), and then Bihar to the Nitish Kumar-led grand alliance, both causing a major setback to the party.
Javadekar also said that terms of many BJP state presidents were about to end, and the process to elect new presidents will start soon, but the decision on Assam was taken first because of the assembly elections.