They ruled that the Welsh Rugby Union acted correctly within all regulations and according to proper procedure over the issue. An appeal by the Scottish Rugby Union questioning the decision of the IRB Regulations Committee was therefore dismissed.
Under the IRB Regulations Committee decision, Shingler was deemed to have been captured by Wales having represented the Wales Under 20 team against the France Under 20 team in a 2011 Six Nations fixture. Both Wales and France had individually designated their Under 20 teams as their next senior national representative teams, as is permitted by IRB Regulation 8.
In a separate decision the IRB Council confirmed the status of Under 20 teams as being eligible for nomination as next senior national representative teams, meaning that any player playing in an Under 20 match in which both teams have been nominated will continue to be captured for eligibility purposes for the nation they appear for.
The WRU's Head of Legal Affairs, Rhodri Lewis, said: "We are delighted that the IRB Council has ratified the decision of the IRB Regulations Committee, that confirmed that the Welsh Rugby Union had complied fully with all of its obligations under the IRB Regulations. It was extremely important to achieve clarity on matters relating to the regulations regarding player eligibility for both governing bodies and players."
The WRU Head of Rugby, Joe Lydon, added: "It was vitally important that the WRU defended its stance over this issue. It was certainly not just about the individual player concerned but a case of needing total clarity on the situation, both retrospectively and going forward.
"The key factor for us was determining that we have acted properly, and continue to act properly as a governing body over this issue. If we had left any doubt over this debate then many players, across many Unions, would have been left in a state of confusion over their international status.
"The IRB ruling has now been confirmed and the WRU will continue to follow the operational policy we already have in place which ensures all players are fully informed of the IRB regulations and their status within them."