Michael Shanks won the Rutherglen and Hamilton West seat after securing more than twice the votes of his SNP rival Katy Loudon.
Thursday’s by-election saw the SNP’s majority overturned by Labour after Mr Shanks won 17,845 votes, well ahead of the 8,399 votes returned for Ms Loudon.
The results give the new Labour MP a majority 9,446 - with Mr Shanks having polled more than 58% of the votes cast.
UK Labour leader Sir Keir Starmer had meanwhile insisted a win for his party in the seat would be an "historic victory" which could be a "milestone" on Labour's journey back to power.
The loss of the seat to Labour also heaps further pressure on SNP leader and Scottish First Minister Humza Yousaf - who has seen his party's fortunes decline in the polls in the wake of the ongoing police investigation in SNP finances.
Report by Caponm.
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