Boston general manager Don Sweeney announced the moves Tuesday. Miller's extension will run through the 2019-20 season and have a cap figure of $2.5 million per year. He entered the offseason as an unrestricted free agent.
The Bruins also signed forward Seth Griffith to a one-year, two-way contract carrying a cap figure of $625,000.
The 28-year-old Miller just completed his third season in Boston, appearing in a career-high 71 games. He also set career bests with five goals, 13 assists and 18 points. Griffith appeared in four games for Boston this season, accruing one assist.
Sweeney also announced the hiring of Bruce Cassidy and Jay Pandolfo as assistants, joining Joe Sacco and Bob Essensa on Claude Julien's staff. In addition, longtime assistant Doug Jarvis will not return for the 2016-17 season.