CCTV evidence played at the tribunal showed the thief throwing a punch at Hehir.
“I noticed him making a left swing, so on instinct I retaliated with a right,” the 62-year-old said.
Both Hehir and the passenger were arrested over the altercation, which happened between Wembley and Maida Vale.
Hehir, who is originally from County Limerick and now lives in Wembley, was later released and told he would not face further police action.
The day after the incident, on 25 June 2024, Hehir was suspended from duty and told to attend an investigation. He was later dismissed.
The subsequent employment tribunal heard from the Met Police, which said Hehir’s response had been “proportionate and necessary in the circumstances”.
A Metroline spokesperson said: “The Independent Employment Tribunal has upheld the dismissal as fair.
“The claimant breached protocols designed to keep staff and passengers safe, which is our priority.”