Bass opted out of the final year of his previous contract in order to secure a longer-term deal, but expressed a strong desire to return to Boston throughout the latter part of the season.
Bass appeared in 59 games last year -- including 39 starts as he moved to the starting power forward role in the second half of the season -- and averaged career-highs of 12.5 points and 6.2 rebounds per game.
The Celtics acquired Bass from the Orlando Magic last season in a sign-and-trade deal in exchange for Glen Davis. Boston was reluctant to offer Davis a long-term deal (he signed for four years, $25.7 million), but they are clearly more confident this time around with Bass.
Having already secured a three-year extension with Kevin Garnett, the Celtics have reassembled their starting five from last season, pairing Bass and Garnett alongside Rajon Rondo, Avery Bradley, and Paul Pierce.
The Celtics are still hoping to bring back top reserve Ray Allen, who gave up his starting role to Bradley late last season. Allen visited the Miami Heat Thursday and it appears to be a tug of war between the two teams to land his services (barring a late entrant).