Lisa Scaffidi will stand for a third term as Lord Mayor, pitting her against City of Perth councillor Reece Harley.

Ms Scaffidi formally declared her candidacy on Tuesday, ahead of Thursday's deadline for local government election nominations.

Even before her bid for re-election was announced, a campaign website headed "Lisa Scaffidi for Lord Mayor of Perth" had gone live.

"Lisa won her second term as Lord Mayor in October 2011 and is seeking a further term to complete the vision that has transformed Perth," the website reads.

Mr Harley, 28, described running against Ms Scaffidi as a "daunting challenge".

"This will be a David-and-Goliath battle against a two-term incumbent Lord Mayor," he said.

Mr Harley, a staunch critic of council clothing allowances, said it was the right time to run and believed the people of Perth were ready for change.

He also dismissed as "a personal smear campaign against him" rumours that he was being financially backed by unions.

"I've received no support whatsoever from political parties or unions, nor have I asked for their support," he said.

Lisa Scaffidi's campaign website for a third term as Lord Mayor went live before her candidacy was announced. ( ABC News )

"I'm not a member of any political party."

Mr Harley said his campaign would focus on reducing the red tape facing many small businesses that wanted to open and make the city more vibrant.

He also pledged to try and help reduce the congestion crisis plaguing Perth.

Curtin University research fellow Jemma Green has also nominated to run as a City of Perth councillor.

She said she was not linked with any political parties and would run as an independent candidate.

The former investment banker and sustainability expert has been an outspoken advocate for light rail and said she was keen for it to be a key council election issue.

Ms Green said light rail had been talked about for too long and that it was time to investigate ways to involve the private sector in its delivery.

"We've done a great job in making Perth more lively in the past decade, and I think the next stage of growth is about making it more liveable and also economically diversifying the city so we're not so reliant on the resources sector," she said.

"I'm really interested in seeing what can be done at the local government level to position Perth and have a vision for Perth that's around Perth as a city of innovation."