Fillmyer signed a minor-league contract with the Diamondbacks on Wednesday, Jeff Passan of ESPN.com reports.
The 26-year-old last appeared with the Royals in 2019 and had an 8.06 ERA, 1.79 WHIP and 15:12 K:BB over 22.1 innings. Fillmyer should provide organizational pitching depth for the Diamondbacks.