Rupani got 81,092 votes, while Congress candidate Jayanti Kalaria managed 57,352 votes.
Interestingly, voters in the seat chose NOTA (None of the Above) as the third alternative, as 3,110 votes were polled in its favour.
NCP candidate Bhavesh Lokhil stood fourth with 1,027 votes. The remaining candidates could not cross the three-digit mark.
There were nine candidates, including six independents, in fray apart from the nominees of BJP, Congress and NCP. However, the main electoral battle was between Congress and BJP.
As per the figures of the Election Commission, out of the total 2.90 lakh registered voters in the seat, 1.42 lakh exercised their franchise during the bypoll.
The seat, once represented by Prime Minister Narendra Modi, who had then entered Gujarat politics, fell vacant following the resignation of sitting MLA Vaju Vala after he was appointed Governor of Karnataka. The constituency has been BJP's pocket-borough since 1990.
Gujarat Chief Minister Anandi Patel recently said that the Rajkot-West by-poll was an issue of prestige for BJP and had asked the party workers to work hard to retain it.
Soon after the victory, Patel thanked the people of Rajkot and also congratulated the winner, on her twitter post.
"Thankful to people of Rajkot for reposing their trust in BJP in assembly by-election & Congratulations to Shri Vijay Rupani for the victory," she tweeted.
Rupani gave all the credit to BJP workers for the win.
"It is only because of the hard work of the BJP workers that the party has succeeded in retaining its bastion. People of Rajkot did not fall for the negative propaganda of Congress and they cast their votes as per their understanding. This is the result of that," Rupani said.
When asked whether he sees any post in Chief Minister Anandi Patel-led state government, he said, "I have been serving people for so many years and will be doing the same in the future also without having any desire for any post."
Meanwhile, Congress nominee Jayanti Kalaria accepted the defeat and said he will continue to raise the issues of poor water-supply and deteriorating condition of law and order in Rajkot.