The 28-year-old man was the rider of a black motorcycle which collided with a grey Vauxhall Corsa in the city centre at around 8pm on Sunday.
Both vehicles are believed to have been travelling in the same direction along Railway Street towards Cross Catherine Street when they crashed.
A West Yorkshire Police spokesman said: "The rider of the motorcycle, a 28-year-old man, was taken to hospital with serious injuries. He remains in hospital in a stable condition.
"The driver of the Corsa, a 20-year-old woman, was uninjured."
Now officers want to hear from anyone who saw either vehicle travelling in the time before the incident orr who witnessed the collision itself.
Contact PC Lisa Gibson at the Eastern Area Safer Roads and Neighbourhoods Support Team via 101, quoting 13170372958.