Sylvie Bergeron was found dead in her apartment on Saint-Joseph Street East on Nov. 30, 2010.
Police said the man they are searching for may have been the last person to see Bergeron alive.
The witness is described as black, in his twenties or thirties, about five feet seven inches and clean-shaven.
Officers said he speaks French without an accent and may have been a student at the time of the murder.
Anyone with information is being asked to contact Quebec City police.
The reward is being offered thanks to the Sun Youth Organization.