This is the second year in a row that Castillo has signed with the Nats in the offseason, but the backstop opted out of the 2020 season due to COVID-19 concerns.
Castillo, 33, will look to solidify the second catcher spot on the roster alongside Yan Gomes. Castillo played at least 100 games from 2013 to 2016 and then 96 games with the Orioles in 2017. His last two campaigns were with the White Sox, where he hit a combined .230 with 18 homers and 56 RBIs.
Tres Barrera will also get a shot at the second catcher spot heading into 2021, but Castillo has 10 seasons of major league experience, appearing in 726 career games with the Cubs, Mariners, Diamondbacks, Orioles and White Sox.
Guerra, 35, pitched 15 2/3 innings over 14 games during 2020 with the Nats, recording a 4.02 ERA with 13 strikeouts and seven walks. In 2019 with the Nats, Guerra went 3-1 with one save and a 4.86 ERA over 53 2/3 frames. His career ERA is 3.73.
The moves provide opportunities to the kind of veterans with experience that general manager Mike Rizzo likes to add each season. There is no guarantee that either or both Guerra or Castillo will make the opening day roster, but their presence in the organization allows Rizzo to focus on acquiring another big bat or two to reignite the Nationals offense.
The Washington Post was first to report the signing of Guerra and USA Today was first with the Castillo news.