Henson, who is currently without a club after failing to secure a new contract with French club Toulon, starts at inside centre, has not represented Wales since the 2009 Six Nations campaign finale against Ireland.
However, the 29-year-old will win his 32nd cap this weekend and has 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.
Henson has never played in a World Cup, and Saturday's Millennium Stadium encounter starts Wales' pre-tournament preparations, which continue with August fixtures against England (twice) and Argentina.
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."
Fly-half Stephen Jones will win his 100th cap, joining Gareth Thomas as Wales' second international centurion, lining up in a back division that also includes his fellow Scarlets Morgan Stoddart, George North and Jonathan Davies.
Cardiff Blues flanker Sam Warburton captains a team that sees Newport Gwent Dragons number eight Toby Faletau and Ospreys prop Ryan Bevington make their Test debuts, with three more uncapped players on bench duty - Dragons hooker Lloyd Burns, Blues prop Scott Andrews and Scarlets centre Scott Williams.
Faletau's fellow Dragons - wing Aled Brew and lock Luke Charteris - gain recalls, with back-row regular Ryan Jones starting in the second-row alongside Charteris.
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.
The Barbarians line-up, which will be announced on Thursday, is likely to include Wales international forwards Martyn Williams and Iestyn Thomas.
Wales team: Stoddart (Scarlets); North (Scarlets), Davies (Scarlets), Henson (unattached), Brew (Newport Gwent Dragons); S Jones (Scarlets), Phillips (Ospreys); Bevington (Ospreys), Bennett (Ospreys), James (Ospreys), R Jones (Ospreys), Charteris (Newport Gwent Dragons), Lydiate (Newport Gwent Dragons), Warburton (captain, Cardiff Blues), Faletau (Newport Gwent Dragons).
Replacements: Burns (Newport Gwent Dragons), Andrews (Cardiff Blues), AW Jones (Ospreys), Turnbull (Scarlets), Knoyle (Scarlets), Priestland (Scarlets), Williams (Scarlets).
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