Labor has secured a majority in the South Australian parliament after winning a nail-biting and unprecedented victory in the Fisher by-election.

Final counting in the southern suburbs seat was completed today (Saturday), with Labor’s Nat Cook edging out the Liberals’ Heidi Harris by 23 votes on a two-party preferred basis.

Cook, a high profile community campaigner, will succeed independent Bob Such, who died in October after representing Fisher for 25 years.

The win will give Labor an outright majority of 24 seats in the House of Assembly, meaning Jay Weatherill’s government no longer needs the votes of independent Cabinet ministers Geoff Brock and Martin Hamilton-Smith to pass legislation.

Political scientists are struggling to find a precedent for a fourth-term Government winning a by-election with a swing to it.

Premier Jay Weatherill claimed victory this afternoon, saying that Cook “ran a positive and effective campaign”.

“In the end, Labor won Fisher because we ran the best candidate with a positive agenda and I look forward to working with Nat in Government,” Weatherill said.

This article was first published as Labor clings to tiny Fisher lead.