The 27-year-old winger, who joined the current Eredivisie leaders in 2008, will head to England after a decade in Holland, having initially signed for Feyenoord.
Spells with Excelsior and NEC Nijmegen followed before he joined AZ, with whom he won the title in his first season.
He is ready to head to the Premier League, though, and said: "I am delighted to have agreed terms with Aston Villa and I am looking forward to joining up with the team in the summer.
"Villa have a long and prestigious history in English football and a fantastic set of fans."
Holman has won 53 caps for Australia and was named by the country's football writers as player of the year for 2011.
"Brett is a very intelligent player, a great team player and a man who is recognised in the game as a non-stop, committed wide midfielder player," Villa boss Alex McLeish said.
"He has international experience and has played in the Champions League. He will add significantly to the experience in the Villa squad."
Source: PA
Source: PA