Smith, who would have been a free agent after the 2014 season, is making $4.5 million this year.
Smith takes a team-best .281 average into Wednesday's series finale against the Reds at Petco Park. He had three hits in Tuesday's 8-2 victory, including his ninth home run of the season. Smith has 25 RBIs, an on-base percentage of .384 and a slugging percentage of .506.
Nice trade by Byrnes and good plan to keep him for a couple years at that price.