- Bats Left, Throws Right
- Height 6' 2", Weight 215 lb.
- School Central Connecticut State University
- High School Wethersfield High School
Ryan Costello was drafted by the Seattle Mariners in the 31st round of the 2017 amateur draft, out of Central Connecticut State University. He began his pro career that year with the AZL Mariners, hitting an outstanding .331/.430/.634 in 44 games. He moved on to the Midwest League and the Clinton LumberKings in 2018 where he hit .266 with 16 homers and 70 RBIs in 101 games. On July 30th, he was traded to the Minnesota Twins alongside Chase De Jong in return for veteran major league reliever Zach Duke. He finished the year with the Fort Myers Miracle of the Florida State League, where he hit .229 in 27 games. He hit a decisive three-run homer in Game 4 of the league's championship series against the Daytona Tortugas, giving Fort Myers the title.
Ryan was back with Fort Myers at the start of the 2019 season, then after 68 games earned a promotion to AA and the Pensacola Blue Wahoos of the Southern League, hitting AA barely two years after being a late draft choice. Combined, he hit .223/.343/.412 with 15 homers and 46 RBIs. After the season, the Twins sent him to the Australian Baseball League to play winter ball. However, a week after joining the only Kiwi team in the league, the Auckland Tuatara, he died suddenly. He was found in his hotel room after not showing up for a practice, his death apparently the result of natural causes. He was just 23.
- Liz Roscher: "Twins prospect Ryan Costello found dead in New Zealand hotel room at age 23", Yahoo! Sports, November 18, 2019. 
- Daren Smith: "Twins' Costello found dead in New Zealand: Infield prospect was set to play in Australian Baseball League", milb.com, November 18, 2019.