The 31-year-old is regarded as one of the quickest bowlers in the world and made a big impact during his first spell with Essex in 2013.
The Eagles reached Finals Day that year and Tait took 4-29 to help them to a 47-run win over Notts Outlaws in the quarter-finals.
Essex coach Paul Grayson said: “Shaun had such a positive impact around the club during his first spell.
“We believe we have an excellent chance of winning the NatWest T20 Blast this season, and Shaun will help us towards that target.
???Alongside Jesse Ryder (of New Zealand), we now have two really exciting overseas players.
???In the LV= County Championship we are intent on giving our younger players a chance and our focus is very much on youth.
???In the Twenty20 competition, we want to use all our experience in this format and go all the way.???