Porte ruled himself out of next Sunday's event in Innsbruck, Austria, with sickness, but Schultz's selection means that there is no place for the already-overlooked Michael Matthews.
Schultz, 24, has spent the last two seasons with the Spanish Pro Continental team Caja Rural-Seguros RGA, but has recently signed a two year-contract with Mitchelton-Scott, starting next season.
Schultz finished 75th overall at the Vuelta a España earlier this month – his second Grand Tour, having also finished the Vuelta with Caja Rural last season – and was third at the GP Miguel Indurain one-day race in March, behind winner Alejandro Valverde (Movistar) and Mitchelton's Carlos Verona.
"It is an honour to be selected to represent Australia at the World Championships," Schultz said in the Australian federation's press release. "I will give my maximum to deliver whatever is required. I would also like to wish Richie a speedy recovery and thank Cycling Australia for their faith in selecting me."
Upon signing him to Mitchelton-Scott, head sports director Matt White described Schultz as "a real climbing talent", which backs up Australian national team selector Brad McGee and Australian Cycling Team Performance Director Simon Jones' decision to draft the youngster from Brisbane onto the team.
"Nick is coming into the team in a specific climbing support role," explained Jones. "He has just completed the Vuelta and he has the form and desire to contribute to the team strategy. I want to thank Nick for taking up this late opportunity."
However, Michael Matthews' (Sunweb) surprise omission from the Australian national team when it was first announced in August led many to be believe that, following Porte's announcement this weekend that he would not recover from illness in time to be competitive for the road race, Matthews may have been given the nod.
It was all-the-more likely given Matthews' form, with the 27-year-old recently winning both the GP Cycliste de Québec and the GP Cycliste de Montréal WorldTour events in Canada.
Speaking to Cyclingnews after the team time trial Worlds event in Innsbruck on Sunday – but ahead of Cycling Australia's announcement of Schultz as Porte's replacement – Matthews had said that he'd be ready if he was called up to replace Porte.
"At this point, I've still heard nothing from the selectors, so I don’t want to push. If they feel like they need me, then I'll come. But till now, I've heard nothing," Matthews said.
"I'm going to be in Livigno [in Lombardy, Italy], so it’s not very far away. I think it's only a three-hour drive. I'm going to spend a week there with my family and enjoy it. If I get the call in the next few days, it's possible, but I guess towards the end of the week my motivation will go down."
Schultz will now join Simon Clarke, Rohan Dennis, Jack Haig, Chris Hamilton, Damien Howson, Rob Power and Rory Sutherland as part of the eight-man squad for the road race on September 30. Dennis will represent Australia in the time trial on Wednesday.