The St. Louis Cardinals selected Weaver in the first round with the 27th overall pick of the 2014 Major League Baseball draft. He signed with the Cardinals on June 16 and made his professional debut for the GCL Cardinals. He was promoted to the Palm Beach Cardinals on August 1. In six starts between the two teams, he was 0–1 with a 7.71 ERA and 2.04 WHIP.
