The Hitech rookie led from pole, with the formation lap starting behind the safety car before a rolling start. He rapidly built up a strong lead to second-placed Victor Martins, with a 2.3s gap by lap eight.
Despite a safety car on lap 21 closing the gap, the young Red Bull junior held on to secure his second win in as many weekends, having also taken victory in last weekend’s sprint race at Silverstone.
Championship leader Martins held second for ART, while Prema Racing’s Ollie Bearman held off team-mate Arthur Leclerc for his third series podium.
Wet conditions saw running start behind the safety car, while Alexander Smolyar stalled on the grid from 16th.
Prema’s Jak Crawford made it past Franco Colapinto (VAR) and the Trident-run car of Zane Maloney on the first lap to move into eighth, while Caio Collet was also up two places into 10th for MP Motorsport.
Martins was close to Hadjar’s gearbox by lap three, with a wobble from the leader allowing his fellow Frenchman to close the gap, but he pulled away again quickly.
David Vidales and Pepe Marti made contact at Turn 3 as Marti tried to move around the outside on lap seven, but the pair both carried on.
Collet was gaining on Maloney by lap nine and almost got past at Turn 3 for ninth, but was forced to wait several more laps to get the move done, with the pair making contact briefly at Turn 1 on the 11th tour.
Hadjar led by 2.5s by the halfway mark, with another 2.5s from Martins to Bearman.
The yellow flags were waved on lap 15 after Charouz team-mates Zdanec Chovanec and Francesco Pizzi collided at turn 10, with Federico Malvestiti spinning behind them. Pizzi was handed a 10s penalty for causing the collision.
Three laps later, the yellow flags were waved again after Zak O’Sullivan was spun by Pepe Marti, who suffered a broken front wing, with David Vidales also making contact with the pair.
The Charouz battle continued despite the earlier contact, with Chovanec and Pizzi again making contact on lap 21, causing a safety car. The pair touched at Turn 4, with Chovanec shunted into the air before ending in the gravel trap.
Racing resumed two laps later, with Jonny Edgar and Crawford making contact at Turn 1, with Stanek and Kaylen Frederick also colliding. Though the pair kept running, Frederick suffered damage and was out at the following turn into the gravel.
Maloney took fifth, with Stanek in sixth and Colapinto seventh. Smolyar took eighth, having started in 16th, with William Alatalo and Ido Cohen rounding off the top 10 for Jenzer Motorsport.
F3 Austria: Full feature race results
