"In the very first chance they get, this is how voters react to opportunist politics and stealing of mandate by rejected parties and coming together for the sake of power. Karnataka by-poll results prove that people won't tolerate if someone tries to play with public mandate and wish," Fadnavis tweeted.
"Many congratulations to BJP, Karnataka BJP, Prime Minister Narendra Modi, Home Minister Amit Shah and (BS) Yediyurappa," he added.
While BJP candidates have been declared as winners from the Yellapur, Ranibennur, Vijayanagara, Krishnarajapete and Chikkaballapur among other constituencies, its candidates are leading on two more seats.
The elections were held for 15 Assembly seats which were left vacant after the legislators resigned in July, triggering the collapse of the Congress-JDS coalition and paving the way for the BJP to come to power.