The 30-year old right-hander was 15-15 in two seasons with the Marlins, who acquired him from Cincinnati in January 2017. He was limited to 23 starts last year, when he went on the injured list twice because of forearm and oblique strains.
Straily had a 5.94 ERA over 16⅔ innings in five spring training appearances. He is 42-36 with a 4.23 ERA in seven major league seasons.
Entering this season, all five members of the Marlins' starting rotation are 27 or younger.
"We're going to be built with our starting pitching," Miami president of baseball operations Michael Hill said Monday. "These guys are part of our future, and we want to give them every opportunity to continue to grow and to get better, help us win ballgames."
The Marlins saw improvement in the breaking balls of Trevor Richards and Pablo Lopez, a better delivery from Sandy Alcantara and a healthy Caleb Smith. They have named Jose Urena their Opening Day starter.
"We have five starters that we really like," Hill said. "We have depth at Triple A that we really like and Double-A and high-A."
Miami is sending Wei-Yin Chen to the bullpen. Manager Don Mattingly said Chen will make some spot starts if needed.