The 30-year-old, who has two Test caps, will be with Paul Grayson's side initially until the end of July.
"I am delighted to have signed a contract to play for Essex this summer," he told the club's official website. "The 2012/13 season has been an amazing one for me fulfilling my ambition of playing international cricket and I am now able to achieve one of my other major cricketing ambitions by playing county cricket."
The LV= County Championship Division Two side struggled to make top-order runs last season and Grayson was delighted to add the left hander to the Essex ranks.
"It's an exciting signing for the club. Initially, he is coming over for the start of our season and will probably be with us until the end of the Friends Life t20 competition," he said.
"We'll revisit the situation then because obviously Australia are touring over here and he wants to try and make a big impression with them.
"I've met Rob and spoken to him a few times, he's a quality player and a very good man who comes highly recommended from some good people that we know.
"He's desperate to play county cricket which is great for us and he comes across as an extremely good team player as well and we are delighted to bring him to the club.
"I'm sure he will have a positive impact on the team."
Quiney has scored more than 3,000 first-class runs including seven centuries and 16 half-centuries.