The move comes as DT Vincent Taylor needs ankle surgery and will land on injured reserve.
Johnson, 27, was a fourth-round pick of the Vikings in 2017 out of Iowa. He played out the final year of his four-year, $3.07 million contract that included a $678,360 signing bonus.
Johnson was testing the open market as an unrestricted free agent for the first time in his NFL career and signed on with the Texans back in April. However, Houston released him during final cuts.
The Saints signed Johnson on to their practice squad just last week.
In 2020, Johnson appeared in all 16 games for the Vikings and recorded 44 tackles and 1.5 sacks.