The serious accident occurred just after 10:30 a.m., and the Roseville Road was closed until nearly 2 p.m. Saturday for the investigation, police said.
Westport Police, EMS, and Fire Department were dispatched to the scene.
The cyclist sustained serious injuries, although the nature and extent were unknown early Saturday afternoon, police said.
The bicyclist was treated at the scene by EMS and fire personnel, then transported to Norwalk Hospital for further treatment, police said.
Due to the possible seriousness of the injuries, the Westport Police Accident Reconstruction Team was called in to lead the investigation, police said.
Roseville Road was closed between Colony Road and Post Road East, and will likely remain closed into the early afternoon, police said.
The pickup truck's driver, who was not injured, remained on the scene and was cooperating fully with the investigation, police said.
Click here to follow Daily Voice Westport and receive free news updates.