Hay, 47, was a Challenge Cup winner with Rhinos in 1999.
He began his playing career at hometown club Castleford and also featured in the top-flight for Sheffield Eagles and Widnes Vikings before moving into coaching.
The Great Britain international had spells on the backroom staff at Tigers, Hull FC and Salford Red Devils and was in charge at Featherstone from 2014-2015.
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He emigrated to New Zealand to lead the coaching and development department at Auckland Rugby League before moving to Germany last December.
Hay’s initial goal is to help Germany qualify for the 2025 Rugby League World Cup in France.
“I will be utilising all of my experience to help grow the game here,” he said.
“The foundations put in place - coupled with the ambition of Bob Doughton, president of Germany Rugby League - provide a solid group of players and coaches to work with.
“Once the full lifting of Covid-19 restrictions allow, we will be looking to grow their knowledge of the game and develop them as a group.
“There are a few international games planned for the end of this year and it will be a great opportunity for me to get a baseline of what we have going forward.”
Germany will face Netherlands in the annual Griffin Cup clash on Saturday, October 2, in Dusseldorf.
Doughton said: “I know from the extensive discussions I’ve had with Andy that he is going to contribute enormously to our development as an organisation and to our on-field performances.
“We cannot believe our good fortune in having someone of Andy’s calibre join our team.”
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