Jim McMahon and Colorado Rockies second baseman Ryan McMahon are related. McMahon was born on December 14, 1994, to his father Jim McMahon, and his mother Tracy McMahon.
McMahon had stated that it was his father who had encouraged him to sign with the Colorado Rockies when he had doubts about signing.
McMahon was a student at the Mater Dei High School and participated in football and baseball as sports piqued his interest in a big way. The Rockies selected him with the 42nd overall choice in the second round of the 2013 Major League Baseball draft.
He signed with the Rockies leaving his dream to play collegiate baseball at the University of Southern California, McMahon made his professional baseball debut with the Grand Junction Rockies.
McMahon signed with Hartford at the start of 2017. He began to play second and first base in addition to third base to increase his versatility. In June, he was given a promotion to the Albuquerque Isotopes. In July also, he participated in the All-Star Futures Game.
The Rockies promoted McMahon to the major leagues on August 11, 2017, primarily so he could play first base. He was back down on August 18 and then called up again in September.
He participated in 119 games at the plate for Hartford, Albuquerque, and Colorado, batting 355/.403/.583 with 20 home runs and 88 RBIs in addition to 17 games for Colorado. He also played in 17 games for Hartford.
On March 21, 2022, McMahon and the Rockies agreed to a six-year, $70 million deal.