The 75-year-old takes over from Barry Robson, who was dismissed last Wednesday, with the club currently sat eighth in the cinch Premiership.
Warnock said: “I’m really looking forward to the challenge here at Aberdeen.
“I’ve made no secret of the fact I’ve always wanted to manage in Scotland so when I spoke to (chairman) Dave (Cormack) and (chief executive) Alan (Burrows) and they asked me to help out it just felt like the right opportunity.
“By all accounts there is a good group of lads here and it’s my job now to get the best out of them.
“Aberdeen is a big club with clear ambition and I’m hoping that during my time here the supporters will get behind the team and I can put a smile on their faces.”
Warnock has been in charge of 15 different clubs over more than four decades of management and came out of retirement 12 months ago for a second stint at Huddersfield.
He steered the Terriers to safety in the Sky Bet Championship before departing in September after taking charge of his last game against Stoke.
Aberdeen chairman Cormack told the club website: “From the moment we first spoke with Neil his enthusiasm for managing Aberdeen was infectious.
“He has had an incredible career in management, not only in terms of volume of games and winning promotions, but also of coming into clubs at short notice and making an immediate impact.
“We look forward to Neil, Ronnie (Jepson) and the team pushing hard in the remaining four months of the campaign as we still have a huge amount to play for both in the SPFL Premiership and the Scottish Cup.”
The Dons earned a 1-1 draw against Premiership leaders Celtic on Saturday and Warnock’s first game as manager sees the team travel to Ibrox on Tuesday where they face Rangers in the league.
He is a short-term replacement for Robson, who followed Derek McInnes, Stephen Glass and Jim Goodwin in leaving the role of Aberdeen manager around this time of the year in four seasons running.
Warnock’s appointment until the end of the season also gives time for Aberdeen to complete their “planned detailed review of the football operation” that began last year and will help the club in selecting a new management team ahead of the new season.
Cormack added: “Ambitious clubs regularly invest in independent advice to support internal coaching, data analysis, recruitment, and medical teams with the goal of improving performance through continuous learning and development.
“The highly experienced team of independent advisors, who do this work with some of the best clubs across the globe, will make recommendations to allow us to understand what we can improve upon in terms of best practice going forward.
“The review will include benchmarking the club against similar teams that currently outperform us in Europe.
“With this work well under way, and due to be completed by early April, we are aiming to have a new management team confirmed by the end of the season.”