Walsh was a placekicker with the Georgia Bulldogs 2008-2011. He was a standout player who amassed a number of significant kicking stats. During his time at Georgia, he thrice made 4 field goals in a game. Twice he attempted a field goal from, his long, 56 yards and converted it once in a game against Coastal Carolina in his senior year. In all, Walsh made 184 of 185 PATs and 76 of 103 field goals. However, in his senior year he made just 21 of 35 field goal attempts. He also had two tackles and one fumble recovery to his credit.
Walsh was drafted by the Minnesota Vikings with the fifth pick of the sixth round. A priority acquisition for the Vikings, Walsh would take over kicking duties for the released Ryan Longwell. Through the first 11 weeks of the season, Walsh missed only one field goal and had another blocked. He was 6-for-6 with kicks over 50 yards and 21-for-21 on extra point attempts. On December 16, Walsh passed Randy Moss for the Vikings' franchise record in points scored by a rookie (119). In his best week of his rookie season, in a game against the St. Louis Rams in week 15, Walsh equalled the NFL record for field goals made from 50 yards or more with his eighth kick (a new team record); his three 50-yarders in the game was also a team record. His 5 kicks also tied an NFL record for most field goals of 37 yards or more in a single game, 5, which only Chris Boniol equaled for the Cowboys in 1996. The next week in a game against the Houston Texans on December 23, 2012, Walsh completed a 56-yard attempt, setting the NFL record for field goals over 50 yards in a season with his 9th 50+ yarder. The 56 yarder also tied the Vikings record of longest field goal set by Paul Edinger in 2005. In the final game of the 2012 season, Walsh completed a 54-yard field goal to make himself 10/10 over 50 yards on the season. He was 3 points short of tying an NFL record for most points in a season by a rookie at 144, Walsh ended 2012 with 141 points for the Vikings; which is the team record. His final regular season field goal allowed the Vikings to beat the Green Bay Packers 37-34 and earn a playoff berth. The field goal also tied the NFL record for most field goals by a rookie kicker at 35 with Ali Haji-Sheikh from 1983.
As reward for his standout rookie season, Walsh was selected for the NFC team in the 2013 Pro Bowl. Walsh was also selected to the All-Pro 1st Team.