Taggart won the A-League's Golden Boot in 2013/14 - scoring 16 goals for the Newcastle Jets – the club United chairman Stephen Thompson had previously shown interested in buying.
The 22-year-old brings with him to Tannadice Park plenty of ability with Terrors boss Jackie McNamara also expecting Royals teenager Kuhl to shine.
"Aaron is with the England Under-20s squad, so we will decide if he is ready to go right into the first-team squad for the Kilmarnock game once he has trained next week," McNamara told the club's official website.
"He's a strong lad and a great passer of the ball.
"He will bring a good presence and his experience of playing in the Championship will be important."