The 29-year-old, who is currently without a club after failing to secure a new contract with wealthy French outfit Toulon last month, will start at inside centre in the match.
Henson has not represented Wales since the 2009 RBS 6 Nations campaign finale against Ireland, but he will now win his 32nd cap and have a chance to start pressing claims for World Cup squad selection later this summer.
Ex-Ospreys star Henson had brief stints with Saracens and Toulon this season, his first competitive rugby since entering a self-imposed exile of more than 18 months from the game following repeated injury setbacks.
Appearances on two celebrity television programmes though, including the BBC's Strictly Come Dancing, ensured he stayed in the media spotlight.
Gatland said: "It is an opportunity for players like Gavin to do his talking on the rugby pitch.
"We have Andrew Bishop, Jamie Roberts, Jonathan Davies and now Scott Williams, but we need depth, and hopefully Gavin does well and he puts some pressure on the established guys.
"He tells us it's fantastic to be back in this environment, that he has really missed it and he is loving his rugby at the moment, and that is a real positive for us.
"He knows he just needs to let his rugby do the talking now."
Henson's selection has somewhat overshadowed Stephen Jones' 100th cap, which he will pick up when he takes the field on Saturday.
Gatland lavished praise on the Scarlets number 10, hailing the "fantastic milestone" which will see Jones become Wales' second cap centurion after former captain Gareth Thomas.
Gatland said: "Stephen has reached a fantastic milestone and he deserves all the plaudits he will get.
"He still has so much more to give, and it is a testament to him that he is still hungry.
"He is not limping towards a century of caps with a sense of relief, but bursting through the landmark, relishing the Baa-baas game but then intent on focusing on the World Cup and the matches ahead."
Cardiff Blues flanker Sam Warburton captains a Wales team that sees Newport Gwent Dragons number eight Toby Faletau, 21, and 22-year-old Ospreys prop Ryan Bevington make their Test debuts.
Gatland is without the services of several front-line players, including Six Nations skipper Matthew Rees, wing Shane Williams, full-back Lee Byrne, centres Jamie Roberts and James Hook, plus prop Adam Jones and lock Bradley Davies.
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