At the 2012 U.S. Olympic Trials in Omaha, Nebraska, the U.S. qualifying meet for the Olympics, Weltz made the U.S. Olympic team for the first time by finishing first in the 200-meter breaststroke with a time of 2:09.01. Weltz also finished fourth in the 100-meter breaststroke with a time of 1:00.68. At the 2012 Summer Olympics in London, Weltz placed fifth in the finals of the 200-meter breaststroke with a time of 2:09.02. His semifinal time the day before (2:08.99) and Olympic Trial time (2:09.01) showed remarkable consistency.