England, who had gone into the clash with a 12-year unbeaten record in Cardiff, were leading 9-8 with four minutes remaining of an error-strewn Six Nations Championship battle in the Millenium Stadium.
But when England skipper Jason Robinson was penalised for failing to release possession in the tackle, British & Irish Lions tour hopeful Henson seized the moment.
Stephen Jones handed the kicking duties to Henson and from 44 metres out he rifled the penalty straight between the posts.
There was no way back for England and the final whistle sparked scenes of wild celebration from a joyous home crowd.
"We needed that and we deserved that," a jubilant Henson told BBC1.
"It's been a long time coming but hopefully we can go on a run now."
Asked how he felt as he lined up his match-winning penalty, Henson replied:
"Very positive. I don't tend to feel the pressure.
"I knew I was going to kick it, I've been kicking those all week."
"As a team we did really well," added Henson, who produced two crunching tackles on England's debut-making teenage centre Mathew Tait.