The Cubs made the announcement Monday and said both players were invited to spring training.
Lopez returns to the Cubs after going 6-6 with a 4.42 ERA in 26 games last season. The right-hander made 16 starts for Chicago.
The 38-year-old Miller is 18-17 with 11 saves and a 4.18 ERA in 694 major league appearances. The lefty pitched for the Cardinals, Blue Jays and Red Sox last season.