Lobaton will report to big league spring training and compete with Kevin Plawecki for a backup job behind Travis d'Arnaud. Lobaton would get a $1.25 million, one-year contract if added to the 40-man roster.
The switch-hitting 33-year-old batted .170 with four home runs and 11 RBI in 158 plate appearances over 51 games with Washington this year, his most since 2014. He is 5 for 18 (.278) with two homers in nine postseason games.
Lobaton has a .218 career average with 21 homers and 103 RBI in eight seasons with San Diego (2009), Tampa Bay (2011-13) and Washington (2014-17).
Swarzak, a 32-year-old right-hander, gets a $1 million signing bonus payable within 30 days of the contract's approval by the commissioner's office and salaries of $5 million next year and $8 million in 2019.
He reunites with new Mets manager Mickey Callaway.
Swarzak spent the first 2+ months of the 2015 season with Cleveland, making 10 appearances with a 3.38 ERA. Callaway was hired to manage the Mets in October after five seasons as the Indians' pitching coach.
Swarzak was a combined 6-4 with two saves and a 2.33 ERA in 70 games last season for the Chicago White Sox and Milwaukee. He had 91 strikeouts in 77 1/3 innings. He has pitched for five teams in the last four years, including Minnesota, Cleveland and the Yankees.
His fastball velocity increased from 93 mph in 2015 to 95 mph this year, according to Brooks Baseball. A four-pitch pitcher through 2014, he was restricted to a fastball and slider by Callaway before bringing back his changeup this year.
Swarzak is 23-30 with a 4.22 ERA over eight seasons. He began his major league career in 2009 with the Twins and was a starter his first year, then began moving into a relief role.