Kussmaul graduated from Fennimore High School and was drafted in the 42nd round of the 2006 June Amateur Draft by the Florida Marlins. Instead of signing, he attended the Madison Area Technical College in Wisconsin and the University of Evansville in Indiana before transferring to Division II Mount Olive College in North Carolina for his last year of eligibility. He amassed a 5-2 record for the Trojans with two complete games, including a 5-hit shutout against 6th-ranked Erskine College. After graduating with a bachelor of science in sociology, he signed to play for the independent Southern Illinois Miners of the Frontier League for the 2009 season. He went 7-2 with 90 strikeouts in 109 innings pitched for the Miners and was signed by the Chicago White Sox in July 2010.
Kussmaul debuted with the Class A Kannapolis Intimidators and was promoted to the Class A+ Winston-Salem Dash after 9 appearances. He remained for the 2011 season with Winston-Salem and was promoted to the Barons at the beginning of 2012. As a Baron, Kussmail made 37 appearances in relief, earning 13 saves in 57 innings with 61 strikeouts and an ERA of 1.11. He was promoted to the AAA Charlotte Knights in September, but appeared in only 1 game, allowing 4 hits and 2 runs in an inning for an 18.00 ERA.
Kussmail returned to Birmingham with the 2013 Birmingham Barons and pitched a total of 33.1 innings in a season interrupted by 83 days on the disabled list for a finger wart. He amassed a season ERA of 2.43 while recording 36 strikeouts and 5 saves. He was selected for the Southern League All-Star Game, but was unable to participate due to injury.
He contributed 2 2/3 critical scoreless innings in game 5 of the Southern League Championship, fanning 6 Mobile BayBears to help the Barons preserve a 4-2 lead. Manager Julio Vinas credited his success to an "erratic delivery" which conceals his fastballs and also makes them seem to move on the way to the plate. He was the first Baron to leave the clubhouse for a victory lap at Regions Field following the win.
- Seiner, Jake (September 16, 2013) "Johnson, Barons rob Mobile in Finals." MiLB.com
- Crenshaw Jr, Solomon (September 17, 2013) "Birmingham Barons' victory lap signals end of first season at Regions Field." The Birmingham News
- Ryan Kussmaul at baseball-reference.com