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.
Now seeded 16th, Williams was drawn into the same section Thursday as No. 1-ranked Simona Halep, the runner-up previous year.
Alex de Minaur, the only Australian men's seed in the draw at number 27, opens against Pedro Sousa, while other prominent first-round matchups for the locals include John Millman against Federico Delbonis, and Nick Kyrgios in a mouth-watering encounter against big-serving Canadian Milos Raonic, the 16th seed. Eighth-seeded Kei Nishikori, who opened the season with a title in Brisbane, is a potential quarterfinal rival and No. 4 Alexander Zverev looms as a semifinal opponent if both players advance that far.
Kyle Edmund, back at the scene of his semi-final appearance 12 months ago, was also given a hard opener at the year's first grand slam against former top-10 stalwart Tomas Berdych, who is unseeded following injury.
"I'm so close, I'll give it a go, " Federer said.
Novak Djokovic, Roger Federer on opposite sides of Australian Open draw
The two had to leave the court to allow for the next practice session. Murray opens against No. 22-seeded Roberto Bautista Agut.
Williams will face Tatjana Maria in the first round, and could meet either Genie Bouchard or Peng Shaui in the second.
Men's top seed Djokovic, who was defending his title when he lost to Istomin, has drawn 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.
It will be the first time for Wang to head into a Grand Slam as a seeded player.
US Open champion Osaka opens against Poland's Magda Linette, and sees last year's upset artist and this year's No.28 seed Hsieh Su-wei, 2018 semifinalist and No.12 seed Elise Mertens and No.6 seed Elina Svitolina in her quarter.
Pep Guardiola responds to Liverpool fans' conspiracy theory
Speaking ahead of City's Carabao Cup semi-final against Burton Albion, Guardiola joked: "I'm not the green-keeper". Asked if Foden could leave Etihad on loan this January, Goal quoted Guardiola as saying: "No way".