Tomic claimed his maiden career title in the Harbour City earlier in 2013, before going on to reach the third round at the Australian Open - where he lost to Roger Federer.
The Queenslander, 21, said his Sydney triumph gave him belief he could claim more silverware in the future.
"Winning Sydney really changed me and made me feel that I can win these tournaments. I'm really looking forward to coming back and having a shot at defending my title," Tomic said.
"I like those moments that come in tournaments when you know you have to prove something and I feel that when the time comes I can play good tennis again in Sydney."
World number five del Potro skipped Sydney this year after only winning two of his four matches there across 2011 and 2012.
The Argentine finished his impressive season with an appearance at the ATP World Tour Finals in London, bowing out in the round-robin stages but taking sets off each of Novak Djokovic and Roger Federer, while posting a win over Richard Gasquet.
Also in the main draw in the week leading into the major at Melbourne Park is Wimbledon semi-finalist Jerzy Janowicz.
In the women's draw, 2013 champion Agnieszka Radwanska also confirmed she will be in the Sydney field in her lead-up to Melbourne.