The Marlins on Tuesday selected the contract of the 5-foot-10, 210-pound right-hander, who was the closer at Double-A Jacksonville.
To make roster room for Ramos, Juan Carlos Oviedo was transferred to the 60-day disabled list.
"I've liked him from Spring Training," Miami manager Ozzie Guillen said. "I think he deserved to be here right now. He earned it. He's one of the best pitchers in the organization. Hopefully we can take a look at him here and see how he responds."
As the closer for the Suns, Ramos had 21 saves. In 68 2/3 innings, he struck out 89 while walking 21.
"Obviously, it's something you work for your whole life," said Ramos, who turns 26 on Sept. 20. "It's a great feeling. You try to take every moment in and enjoy it."
Ramos' velocity has been clocked at 94-96 mph, and he has topped out at 98. He mixes in a cutter, slider and changeup. He's trying to join the list of pitchers under 6-feet tall who have shown they belong in the big leagues.
"I've had to work my whole life," Ramos said. "This is going to be nothing new trying to prove myself and to show it doesn't matter what my height is. I'm prepared to work. I'm prepared to do all the things necessary.
"I try to stay as tall as possible on the mound -- arm angle. Get as much downward plain as possible. Also deception with my front arm -- try to hide the ball a little more -- and the velocity."
Ramos is a fan of pitchers like Atlanta's Kris Medlin, who at 5-foot-10 has been dominant.
"Oh definitely," Ramos said. "I'm always cheering for someone who is around my height. It's like me. I'm always cheering for those guys."