Jo-Wilfried Tsonga looms as a potential second-round opponent in a possible rematch of their AO 2008 decider.
Defending champion Roger Federer is seeded No. 3 after Rafael Nadal, while women's defending singles champion Caroline Wozniacki, who beat Halep in last year's final at Melbourne Park, is No. 3 behind second-seeded and 2016 champion Angelique Kerber.
Cilic has Andy Murray, who is coming back from a long-term hip injury, in his section.
Murray won just two games in an incomplete practice match with Djokovic at Melbourne Park, showing signs he's still not fully fit after spending most of the last 18 months off the tour. But being so close, I'll give it a go.
Men's top seed Djokovic, who was defending his title when he lost to Istomin, will first meet a qualifier in his bid for a record seventh Melbourne title and third Grand Slam crown in succession following wins at Wimbledon and the U.S. Open.
One of the standout matchups of the first round sees unseeded Nick Kyrgios' meet 2016 semifinalist and 16th seed Milos Raonic, with the victor of that contest going through to face either 2014 champion Stan Wawrinka or Ernests Gulbis.
The fan, Australian teenager Jordyn Kollmorgen, posted that Murray, a three-time Grand Slam champion, was the inspiration behind her love for tennis.
"I can't believe it's been a year already", Dane Wozniacki said at the draw ceremony.
During his Australian Open qualifying victory over Jurij Rodionov, Great Britain's Dan Evans pulled off one of the most remarkable shots we can remember seeing.
"To finally get that (title) here was so special, it's the happy slam".
Second seeded Nadal begins against Australian James Duckworth, fourth seed Alexander Zverev faces Slovenian Aljaz Bedene while last year's runner-up Marin Cilic has a tricky encounter with Australian Bernard Tomic.
Serena Williams, who is seeded 16th, faces fellow mother Tatjana Maria of Germany in her first competitive match since her tempestuous US Open final loss to Naomi Osaka.
Murray was drawn against Bautista Agut after struggling against Djokovic on the Margaret Court Arena.