Labor's Brian Mitchell has won the Tasmanian seat of Lyons, according to ABC chief election analyst Antony Green, taking federal Labor's total seats to 75, one short of a majority.
With counting crossing over the 80 per cent mark, Mr Mitchell leads with 50.9 per cent of the vote to the Liberal Party's Susie Bower.
Mr Mitchell's margin is smaller than it was at the 2019 federal election, with the sitting MP courting controversy this time with historical social media posts.
He had previously held the seat with a 5.2 per cent margin but Saturday saw a swing to the Liberal Party after preferences.
Announcing the result, Green said: "We have just given away Lyons, which is the great central seat in central Tasmania.
"Two days ago it was spotted that there was a potential counting error in one of the pre-poll centres.
"All counting centres are counted twice. This was an initial count. It looked like an error, they've rechecked it.
Green said it initially appeared the seat saw an unusually large swing against Labor but, once the error was found, it came down to a normal figure.
"So they (Labor) need one for a simple majority government," he said.
"At this stage we are waiting on what is to come."
The win for Labor in Lyons means all five sitting Tasmanian MPs have been returned to parliament, avoiding a change in any seats.
Mr Mitchell was elected as the member for Lyons in 2016, and was re-elected in 2019 after the Liberal-endorsed candidate opposing him quit the party over controversial social media posts.
Mr Mitchell himself caused a stir this election campaign with his own historical social media posts, including a post from 2011 about female incontinence.
Labor leader Anthony Albanese said during the campaign the post was "not appropriate".
Mr Mitchell also apologised for other historical comments he made online, including one about a colleague "massaging boobies".
The posts were made before Mr Mitchell was elected to parliament.
Mr Mitchell, a former journalist and newspaper editor, called an ABC reporter a "maggot" in 2017.
Mr Mitchell apologised this year and deleted the comments.
"I acknowledge that some of my previous comments have been insensitive," he said.
"I shouldn't have made them and I apologise for them. I've now removed the comments."
Mr Mitchell's election means Labor has 75 seats in parliament, one short of a majority, but four seats are still in doubt.
Labor is currently ahead in the Victorian seat of Macnamara.
