The 20-year-old began his career with home-town club Kidderminster Harriers, for whom he scored twice in forty-five appearances prior to moving to St Andrews in the summer of 2016 for a fee of around £75,000.
He made his League debut on loan at Grimsby Town last season, appearing a further three times for the Mariners.
Maxwell, who is a regular for Blues' under-23 side, will go straight into the Heed squad for tomorrow's match with Aldershot Town at the International Stadium.