The TAI/AgustaWestland T-129 ATAK is a derivative version of the A129, and its development is the responsibility of Turkish Aerospace Industries (TAI), with AgustaWestland as the primary partner.

The A129 Mangusta is the first European attack helicopter; as such it has several original aspects to its design, such as being the first helicopter to make use of a fully computerised integrated management system to reduce crew workload. It was decided that much of the helicopter's functionality was to be automated; as such, parts of the flight and armament systems are monitored and directly controlled by onboard computers. The A129 shares considerably design similarities to the Agusta A109 utility helicopter; the entire rear half of the A129 was directly derived from the A109 and incorporated to an entirely new forward section.

The A129 can be used in the anti-armour, armed reconnaissance, ground attack, escort, fire support and anti-aircraft roles. In the anti-armour role, the helicopter can carry armaments such as up to eight Hellfire missiles. The A129 can also be equipped with 81 mm or 70 mm (2.75 in) unguided rockets and has a M197 three-barrel 20 mm cannon in a turret mounted under its nose.

The A129's fuselage is highly angular and armoured for ballistic protection; the composite rotor blades are also able to withstand hits from 23mm cannon fire. The two man crew, comprising a pilot and gunner, sit in a conventional tandem cockpit. The A129 is equipped with infrared night vision systems, enabling night time operations. Power is provided by a pair of Rolls-Royce Gem 2-1004D turboshaft engines, which incorporates protective measures such as to reduce the helicopter's infrared heat signature.