Makarounas, 22, who started his A-League career with Perth Glory, will be hoping to impress coach Guillermo Amor and cement a starting spot in Adelaide's side.
"It feels great to be an Adelaide United player and I'm excited to get going," Makarounas said.
"Obviously the team was very successful last year and I felt it was time for me to make a change in my career and I'm happy the move has brought me here.
"There are some great players here at the club and the style of football that the team plays is really good and it will suit me very well.
"Watching the team play last season, you could see how attractive the football was, so hopefully I can contribute to the team positively and bring something extra to the squad.
"We want to have another successful year and I'm ready to do whatever is best for the team and play wherever I'm needed."