Garcia will have a base salary of $1 million next season and Thornton $2.25 million.
Garcia was 3-4 with a 4.34 ERA in nine starts after signing a minor league contract June 8. He was a key member of the 2005 rotation when Chicago won the World Series. He will be a candidate for the fifth starter's role next spring.
Thornton, a key setup man, was 6-3 with a 2.74 ERA and four saves this season. He had 87 strikeouts in 70 appearances.
Thornton has compiled a 21-19 record with a 3.71 ERA in six major league seasons, all but one of his 349 games in relief.