The 26-year-old Fuller is considered a key player for Chicago's defense. The tag, announced Tuesday, guarantees Fuller $12.9 million next season.
Fuller can sign an offer sheet with another team, but the Bears get a chance to match it and they are expected to seek a multiyear deal. The team gets no compensation if they choose not to match.
Chicago hasn't used a transition tag since 2001, when it was used on defensive lineman Bryan Robinson.