Sidhu, who was a Congress MLA before deserting the party to join SAD, drubbed Congress nominee Harminder Singh Jassi by a margin of 46,642 votes.
SAD won the Talwandi Sabo Assembly seat by a margin of 46,642 votes, an election office spokesman said here.
Sidhu polled 71,747 votes, Jassi got 25,105 votes, AAP's Baljinder Kaur 13,899 and Independent Balkar Singh 6,305 votes.
The by-poll was necessitated as Sidhu switched sides by leaving Congress and joining SAD.
Jassi, a former Congress MLA, is a relative of Haryana's Sirsa-based Dera Sacha Sauda sect head Gurmeet Ram Rahim Singh.
With the victory, SAD wrested the Talwandi Sabo seat from the Opposition Congress.
Meanwhile, AAP's Baljinder Kaur finished poor third at the hustings.