The 28-year-old becomes the club’s fifth signing of the summer and returns to Pittodrie after a successful loan spell in the second half of last season.
After arriving in January, the striker quickly established himself as a fan favourite and a valued dressing-room presence, making 18 appearances and contributing key goals and assists as Aberdeen finished the campaign strongly.
A former AFC Wimbledon academy graduate, Olusanya has also played for Middlesbrough, St Mirren, Arbroath and Doncaster Rovers before joining Houston Dynamo in 2025.
"I am buzzing to be back," Olusanya said.
"From the moment I arrived in January, I felt welcomed by everyone at the Club. The staff, the players and the supporters all made me feel at home.
"Coming in during the middle of a season isn't always easy. I was still working my way back to full fitness and adapting to a new environment, but I felt I improved as the weeks went on and now I have the opportunity to start again with a full pre-season behind me.
"I know the manager well and I know exactly what he expects from me. That gives me a great platform to push on and show what I can do.