Johnson agreed to a contract with the Reds on Sunday, Jon Heyman of the New York Post reports.
The terms of the deal aren't clear, but Johnson is likely to receive less than the $7 million club option that was declined by Atlanta in November. Johnson recorded one save and 16 holds with a 3.05 ERA, 1.20 WHIP and 59:19 K:BB across 65 innings for Atlanta last year.