Bahuguna as a Congress candidate received 53,766 votes out of the total 69,695 while his nearest rival Prakash Pant managed to get only 13,812 votes in the July 8 by-election, the counting for which was held yesterday.
The victory margin of 39,954 is the biggest-ever margin recorded in the history of Assembly elections in Uttarakhand so far.
Earlier, former Chief Minister N D Tiwari scored a win over his BJP rival Ram Singh Bisht with an impressive margin of 23,220 in Ramnagar by-election in 2002.
Thereafter, B C Khanduri had clinched the Dhumakot seat by defeating Surendra Singh Negi of Congress with a margin of 14,171 in 2007 Assembly by-election.
However, the earlier record of highest victory-margin in any Assembly elections was that of Madan Kaushik (BJP) who had won the Haridwar seat by a margin of 28,640 in 2007 Assembly poll.
Kaushik was followed by state Parliamentary Affairs Minister Indira Hridayesh, who defeated BJP's Renu Adhikari with a margin of 23,583 from Haldwani in the assembly elections held early this year.