Former England sevens player Ryan guided Fiji to a record nine sevens tournament titles, including Olympic gold, after leaving his position as England Sevens coach to take charge of the South Sea Islanders in 2013.
The 45-year-old has a wide-ranging remit to support, advise the programmes and preparation planning of WRU national Age Grade sides and his expertise will be made available to all teams outside of the national squad - which includes the national U20s, national U18s, Women’s national programmes and both men and women’s sevens.
"Ben Ryan's appointment is a real coup for Welsh rugby," said WRU head of rugby performance Geraint John.
"He is a much sought-after high performance coach, who has had significant successes with the Fijian national sevens side.
"We are particularly interested in benefitting from the meticulous attention to detail and major planning experience which Ben showed to maximum effect during the Olympics in Rio."
Ryan, who will also work on coach development at the WRU, said: "I am really looking forward to all that lies ahead."
The Welsh governing body has also brought in Peter Drewett as performance coach manager.