The New Zealander, a left-arm seamer, has signed up for the second half of the campaign
Raymond Tool has joined Essex for the remainder of their Royal London Cup campaign.
The 24-year-old arrives for the final four group games of the campaign having been playing Premier League cricket for Belhus CC in Grays.
A left-arm seamer who can swing the ball, Toole plays for Central Districts back in his homeland. In six Plunket Shield matches last season he took 23 wickets at 25.95.
Essex return to action in the 50-over competition against Glamorgan on Sunday (August 14) before matches against Yorkshire, Worcestershire and Hampshire.
They are already struggling in the race to qualify for the knock-out stage, having won one of their opening four games.
Tom Westley's side are one win from four in the Royal London Cup (Jan Kruger/Getty Images)
Toole's arrival follows the signing of Grant Roelofsen for the duration of the competition.
"It's been a busy few days getting everything sorted but I’m so pleased to be given the opportunity to represent Essex in 50-over cricket," said Toole.
"I've been training with the team at Chelmsford for a few weeks so I’m familiar with the lads and they’ve been really welcoming to me.
"With four games left in the competition, I’ll be hoping to hit the ground running so we can finish the Royal London Cup campaign strongly, and if we do that, you never know what could happen."