Labor will win the inner-city Melbourne seat of Macnamara, handing Prime Minister Anthony Albanese the reins to a majority government.
9News can project Labor's Josh Burns will retain the seat after a tight three-way race against Colleen Harkin for the Liberals and Steph May-Hodgins of the Greens.
The win gives Labor the 76 seats needed for a majority in the 151-seat House of Representatives.
Treasurer Jim Chalmers hailed the result on Monday night, sharing a photo on social media with Josh Burns and the number "76".
Labor may yet solidify its majority as two more seats remain too close to call.
In Gilmore on the NSW South Coast, Labor's Fiona Phillips led Liberal Andrew Constance by less than 200 votes on Monday night.
Just a few hundred votes separated outgoing Liberal assistant treasurer Michael Sukkar and Labor's Matt Gregg in Deakin, in Melbourne's east.
Election night delivered Albanese victory over Scott Morrison as voters deserted the Liberal Party in droves.
But with a historic surge of support for the Greens and the so-called teal independents, it had been unclear whether Labor had the numbers to govern in its own right or would be forced to negotiate with the significantly enlarged 16-seat cross bench.
The result in Macnamara gives Albanese a one-seat majority in the House of Representatives but the makeup of the Senate remains unclear.