The German central defender joins Boro after passing a medical and agreeing personal terms at the club's Rockliffe Park training ground.
Formerly with Eintracht Freising, 25-year-old Haas has made 62 appearances for Bayern Munich's second team, who play in Germany's third tier.
Boro manager Tony Mowbray said: Maximilian was very keen to come here and test himself in English football. It's a challenge for him and his arrival will create additional competition for places in that area of the pitch.
He is a real competitor and comfortable with the ball. The challenge for him is acclimatise to the English game and then take any opportunity that comes his way.
Source: Northern Echo
Source: Northern Echo