Despite winning Grand Slams for Wales in 2005 and 2008, the Ospreys, Saracens and Toulon all struggled to harness his talent on the pitch.
But Thomas was left in no doubt about the benefits of snapping him up for the Blues' RaboDirect PRO12 campaign after Williams delivered a glowing report on Henson's progress at Wales' intensive World Cup training camp.
He said: "It [Henson signing] came to the forefront when I was talking to Martyn Williams when they [Wales] came back from their training camp in Poland.
"He made the comment how amazed and impressed he was with Gavin Henson. I said to Martyn: 'do you think he wants to get back into the game on a serious basis?' He said: 'absolutely'.
"He has always been on our radar and we have always considered him, as I'm sure every rugby fan has in Wales has, as such a world class player.
"Gavin on the world stage is a phenomenal rugby player and we are absolutely delighted to have the opportunity of him joining the Blues.
"And I'm quite sure that he will settle and I'm quite sure as a result of that he will get back to the world-class performer we know he can be.
Both his spells at English side Saracens and Top 14 big-spenders Toulon were brief as Henson struggled to acclimatise to new surroundings after six years with the Ospreys.
Henson followed that by taking a two-year sabbatical from rugby. But despite signing a deal that lasts until the end of the season, Thomas is convinced Henson will finish his career at the Cardiff City Stadium.
"At his age now and stage in life I think Cardiff Blues will be the place where he will play the rest of his rugby," he said.
"I think it's important for Gavin to find his feet and settle in. He has had a difficult couple of years as we well know. It's been well documented.
"He needs all our support now to help him get back to his best and I'm quite sure after this settling in period of eight months Gavin Henson will get a much longer term contract with the Blues."