Southwick originally signed with Brigham Young University out of high school, when he elected to take a two-year Mormon mission. Upon returning from his mission, Southwick enrolled at Oregon State University. Southwick then transferred to Dixie State College for a season. From Dixie State, Southwick transferred to the University of Utah, where he walked-on and was listed as the backup quarterback going into fall camp with the Utes. Southwick then went back to Dixie State. He played his senior season of college football at Occidental. Southwick's college statistics, excluding post-season play, include 271 completions out of 478 passes for 3,804 yards, and 29 touchdowns with 23 interceptions. As a starter in college, during the regular season, Southwick compiled a record of 13 wins and 5 losses.
Professional career
Southwick began his professional career signing with the Louisville Fire of the af2. After finishing the season with the Fire, the franchise folded as well as the Arena Football League. In 2009, Southwick signed with the Oakland Raiders, but was released prior to the preseason. On February 25, 2011, Southwick was assigned to the Dallas Vigilantes, but he was placed on reassignment just 3 days later on February 28. On May 16, 2011, he signed with the Tampa Bay Storm. On July 16, 2011, Southwick made his first career arena football start for the Storm, where he was eventually replaced by Matt Grothe due to his ineffective play. In April 2014, he was named the starting quarterback for the Portland Thunder. On April 7, 2015, Southwick was assigned to the Spokane Shock. On May 13, 2015, Southwick was traded to the Los Angeles KISS for future considerations. He was assigned to the Portland Thunder on February 1, 2016. The Thunder changed its name to the Portland Steel on February 24, 2016. He was placed on reassignment by the Steel on April 25, 2016. On May 26, 2016, Southwick was assigned to the Los Angeles KISS. On June 25, 2016, he was placed on reassignment. On July 6, 2016, he was assigned to the Orlando Predators. On May 23, 2017, Southwick was assigned to the Cleveland Gladiators. On April 19, 2018, he signed with the Massachusetts Pirates. He was released by the Pirates on April 25, 2018. On April 26, 2018, he was claimed by the Jacksonville Sharks. The same day, he was also placed on refuse to report. On May 23, 2018, he was assigned to the Philadelphia Soul. On June 5, 2018, he was placed on reassignment. On April 17, 2019, Southwick was assigned to the Columbus Destroyers. He was placed on recallable reassignment on April 19, 2019. On December 11, 2019, Southwick signed with the Jersey Flight. The 2020 National Arena League season was canceled due to the Covid-19 pandemic.