Marketers have long used celebrity endorsement to help viewers build strong brandproduct associations. Celebrity endorsements increase brand awareness and recall, but how celebrity endorsements shape the decision process remains unclear. A wealth of research indicates that people tend to follow someone else's gaze, yet its effects in advertisements have been largely unexplored. We recruited 77 participants to investigate the effect of celebrities and gaze-cueing in advertisements on both gaze behavior and binary choices. We combined computational modeling with eye-tracking and pupillometry to identify which internal components of processing are affected by celebrity endorsement. We found that gaze-cueing and celebrity endorsement influence gaze allocation and option selection. Further, results from computational modeling, eye-tracking, and pupillometry revealed that the effect of celebrity endorsement on decisions can be explained as an offset in the starting point of an evidence accumulation process as well as changes in the rate of accumulation, thereby biasing choice.