The Cincinnati Reds drafted him in the 9th round of the 2008 Major League Baseball Draft.
He played 2008 for the rookie class Billings Mustangs. He hit .299 with 7 homers and 35 RBI in 254 at-bats. Sappelt had 301 at-bats for Single-A Dayton in 2009, hitting .269 with 3 homers and 25 RBI; in 251 at-bats for the single-A advanced Sarasota Reds he hit .295 with 4 homers and 21 RBI.
Sappelt started 2010 with the Single-A advanced Lynchburg Hillcats. He hit .282 with 0 homers and 4 RBI in 71 at-bats. He was promoted to Double-A Carolina, and hit .361 with 9 homers and 62 RBI in 330 at-bats. He was a mid- and post-season All-Star in the Southern League for the Mudcats, and was named Southern League Most Valuable Player. His performance earned him a promotion to Triple-A Louisville, where he hit .324 with 1 homer and 8 RBI in 108 at-bats for the Bats. His season totals for 2010 were 509 at-bats, .342 average, 10 homers, and 74 RBI. He was named Reds Minor League Hitter of the Year. His season performance earned him a trip to the prestigious Arizona Fall League, where he hit .292 in 72 at-bats with 0 homers and 10 RBI. He also played in the Venezuelan Winter League, batting .305 with 1 homer and 10 RBI in 118 at-bats. He received a non-roster invitation to spring training for 2011.
Sappelt was invited to the major league spring training camp in 2011 as a non-roster invitee. He backed up his award as Reds Minor League Hitter of the Year by hitting .564 (22-for-38), along with three homers and 12 RBI. However, Sappelt was cut from the Reds roster late in spring. Manager Dusty Baker said that a lot of the decision had to do with the fact that Sappelt was not on the 40-man roster, which at the time was full.
Sappelt went back to Louisville for the 2011 season, and continued hitting. Through his first 74 games as the Bats' center fielder, he hit .313 with seven homers and 29 RBI, including a .358 average against lefties.
After Chris Heisey injured his oblique in batting practice and was placed on the 15-day DL, Sappelt was called up to the majors for the first time on August 7, 2011. He made his Major League Debut vs the Chicago Cubs, leading off and playing left field.
On December 23, 2011, Sappelt was traded with Travis Wood and Ronald Torreyes to the Chicago Cubs for Sean Marshall. On May 6, 2013, Sappelt was optioned to the Iowa Cubs. He was designated for assignment on September 3, 2013.
On December 18, 2013, the Philadelphia Phillies signed Sappelt to a minor league contract, that included a spring training invitation.
Sappelt was released from the Olmecas de Tabasco on April 17, 2017. On May 5, 2017, he signed with the Rieleros de Aguascalientes.