Wales's all-time try scorer Williams broke Gareth Thomas's record with his 41st Test score in just 56 appearances to clinch the dragons' second Grand Slam and RBS Six Nations title in four seasons against France.
Williams touched down six times in the competition with braces against Scotland and Italy before scoring successive winners in the Triple Crown clash in Ireland and the championship decider against Les Bleus.
Williams, 31, said: "This is a fantastic end to a phenomenal week. It's been a special championship but this is the icing on the cake. It's an even greater honour to know that this has come from a combination of former players' nominations and fans' votes, whose support throughout this year's championship has been sensational.
"To be up with the greats in Welsh rugby as the highest try scorer is incredible. But is isn't about that, it is about winning the Grand Slam."
WRU Group Chief Executive, Roger Lewis, said: "This is a well deserved honour for a player who has proved his talent with some scintillating performances. The entire squad is a credit to our Nation and Shane's try scoring record speaks for itself.
"This honour reflects on his brilliance and on the standard of play delivered by the squad as a whole in a tournament during which we have seen some fantastic Welsh play.
"Now is the time to reflect on this wonderful success and plan for a future in which I know Shane will be aiming to show the supporters even more of his incredible footballing skills."