Barnes penalised and sin-binned flanker Stephen Ferris for a dangerous tackle on Ian Evans in the final minute at Lansdowne Road on Sunday.
Leigh Halfpenny landed the penalty to snatch victory for Wales and Ferris was subsequently cited.
Ireland's management revealed on Wednesday that the independent Six Nations disciplinary hearing that cleared Ferris also declared Barnes was at fault for awarding the penalty.
But Barnes' decision-making has been backed by the IRB and Six Nations, who released a joint statement expressing satisfaction with the official's performance.
"While an independent Six Nations disciplinary panel did not ultimately uphold the citing, the IRB's match officials performance review endorsed Barnes' decision to award a penalty," the statement read.
"On first viewing the panel could understand exactly how the match referee came to his decision.
"In dismissing the citing no criticism of the referee's on-field decision should be taken or inferred.
"It was only after careful and prolonged analysis of the dynamics of the contact, including slow-motion and step-by-step viewing, that the committee was able to see the strength of the submissions made in favour of Stephen Ferris.
"All match officials are selected for international competition on merit.
"Performances are reviewed on an ongoing basis and taken into consideration when appointments are made for future international competitions.
"Neither organisation will make any further comment on this matter."
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