The 48-year-old Kiwi replaces Martin Whitcombe, whose contract was not renewed by the North One East club.
Posa, who was born in Auckland, has been involved with the successful Yorkshire Under-20 side for the past 14 years, during which time they have won seven national titles, including the past four seasons.
He has also helped Beverley gain four promotions in as many seasons (2003-07) in a player-coach role, plus another as a head coach in 2011-12 during which time the East Yorkshire club rose from Yorkshire Division Two to National League Two.
Since then he has been head coach at Doncaster Phoenix, who won Yorkshire Division One and North One East in successive seasons (2014-16) as well as reaching this season's Yorkshire Cup final.
The RFU Level Three coach has also set up, almost single-handedly, Doncaster Knights' Academy, where almost 40 students are training full-time, 12 of whom are training with the Greene King IPA Championship club.
The Croatian international's success has not been confined to England, however, as he helped Glasgow Hutchesons Aloysians (commonly abbreviated to GHA) to two promotions and has kept Biggar in Premier Division Two rugby for three seasons in Scotland.
In addition, Posa, capped 56 times by his country, has returned to eastern Europe to coach the Croation Sevens team, having also helped top club Makarska Riviera to two championship titles and a national cup.
Posa will start his duties at Wagon Lane in the middle of next month, once he has returned from coaching Croatia's sevens team.
Chris Hemsley, rugby committee chairman with the Bees, said: "We are delighted to have Anthony, who has had so much success in England, Scotland and overseas, on board.
"His long-standing success with Yorkshire Under-20s was as a volunteer, which shows his commitment, and we have a three-year plan under Anthony which will hopefully move us forward on the field alongside our developments off the field.
"We are keeping Richard Tafa involved as a coach and also intend to use prop Ryan Wederall in a player-coach role - the players responded to him last season - with the forwards as he moves towards his 250th league appearance for us.
"Ryan was involved in helping Anthony come on board, and we hope to announce additions to our coaching set up in the near future. as well as some player signings."
* The annual meeting Bradford & Bingley RFC Ltd will take place in the clubhouse next Thursday (6.30pm)
By Bill Marshall
Updated 16:33 - 31 May 2018 by Benji Pickin
Article thanks to The Telegraph and Argus