The Nigeria-born centre half has been training with Rovers for the past few weeks and has been handed a contract until January as Richie Wellens looks to bolster his defensive options following injuries to Tom Anderson and Cameron John.
He is eligible to make his debut in Saturday’s trip to Wigan Athletic.
Olowu joined Arsenal’s academy at the age of eight and remained with the club until the end of last season.
The 21-year-old picked up senior experience with loans at Wealdstone and Cork City.
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Olowu spent time on trial with Manchester United U23s earlier in the summer and played in matches against Chelsea and Manchester City in Premier League 2.
Wellens spotted the defender playing in a friendly for the U23s in early August, with current Rovers loanee Ethan Galbraith also in the side, and he invited him to train with Rovers.
A deal for the youngster was first mentioned several weeks ago but Wellens’ priorities at the time were in recruiting forward players.
The injuries to Anderson and John led to the Rovers board sanctioning the release of further funds in order to secure a free agent defender, with Wellens turning to Olowu.