Having missed out on the final 23 for Australia's squad for the recent World Cup, she joins fellow internationals Lydia Williams and Elise Kellond-Knight in Melbourne.
Gielnik, who has spent the last two years playing for English side Aston Villa in the Women's Super League, rejoins the club she helped to the W-League premiership in 2018/19.
The 31-year-old has spent much of her career playing overseas, including stints with Liverpool, Bayern Munich and Swedish club Vittsjo.
"I'm excited to be back at Victory and working with (coach) Jeff (Hopkins) and the team for the upcoming season," she told the club's website.
"I can't wait to get started.
"I had a great experience during my first stint at the club … and I'm looking forward to achieving more success this season."
Head coach Hopkins welcomed the return of the 54-cap international.
"It's wonderful to have a player of her calibre return to the league and join our squad for the upcoming season," he said.
"We know she will be an important contributor with her experience and guile in front of goal."
The A-League Women campaign gets underway on Saturday October 14, with Victory hosting another of Gielnik's former clubs, the Brisbane Roar, for their season-opener the following day.
2°C