The driver was sprayed in the face with a CS-type substance by a passenger in Armley on Tuesday afternoon.
Officers from West Yorkshire Police were called to the bus stop outside the Pet and Aquatic World store on Armley Road at 2.25pm.
Staff from the ambulance and fire service also attended the scene.
The attacker had tried to get off the bus before the stop and then forced the doors open to leave.
A police spokesman said the driver, a 54-year-old man, experienced stinging to his eyes, nose and throat.
He was taken to hospital to be checked over and is not believed to have suffered any lasting ill effects.
A 20-year-old woman passenger was also taken to hospital after having an asthma attack. She was treated and released a short time later.
Tests have been carried out by the fire service on the substance and it is believed be a CS-type spray or similar.
The suspect is described as white, about 5ft 11in tall and of average build.
He had got on the city-bound number 72 First service at Armley Ridge Road.
He walked off in the direction of Branch Road after the attack.
Insp Sarah Towers, who heads neighbourhood policing for west Leeds, said: “We are keen to hear from anyone who recognises the man shown in the CCTV image or who has any information that could assist the investigation.
“We would also still like to hear from anyone who witnessed the incident or who saw this man leaving the scene or in the general area around the time of the incident.”
Anyone with information is asked to ring 101 quoting crime number 13180156078 or Crimestoppers anonymously on 0800 555111.