Harbhajan, who turned 32 on Tuesday, has been out of Indian team for close to a year now. He will be aiming to get back to the national team through this stint in England.
"There is no cricket here. As a professional, I must stay fit and I am sure I'll hit bowling rhythm soon. County cricket offers four-day cricket and at this time of the year it will help if I get to bowl a lot of overs. This match practice will help me do well in Tests," Harbhajan was quoted as saying by The Hindu newspaper on Tuesday.
"Essex Cricket is delighted to announce that Indian bowler Harbhajan Singh has agreed to join the County for the second half of the 2012 season," a report on Essex website said on Tuesday evening.
"The spin bowler will be arriving mid-July and will be available to play in the outstanding 8 LV= County Championship matches through until the end of the season, plus the county's seven remaining matches in the Clydesdale Bank 40 competition."
"His first appearance is scheduled for the match with Gloucestershire at Cheltenham on July 11th - subject to receiving a UK visa in time," the report added.
Essex Head Coach Paul Grayson said on the website, "We are delighted to have signed one of the best spinners in world cricket over the last 10 years or so. Harbhajan is a great character who is a match winner and I believe that his winning mentality will rub off on the rest of the playing squad here at Essex.
"I am really excited at the prospect of having him in the squad and this signing for the second half of the season shows that Essex mean business and will continue to fight in the LV= County Championship & Clydesdale Bank 40 formats of the game."
Harbhajan has played 98 Tests and taken 406 wickets. In 229 wickets, he has 259 scalps. He last played for India in July-August last year against England in a Test match.