The 37-year-old announced his retirement from frontline international duty last week, having played his 101st and final England game in this month's Six Nations loss against France.
Care, the sixth man to win 100 caps for England, has yet to agree a new contract with London club Harlequins for next season but is now set for at least one more appearance at Twickenham.
"You don't get too many firsts at this stage of your career, but this has been a long time coming!," Care said in a statement issued Thursday.
"It's nearly happened a few times over the last few years, but now the stars have aligned and I cannot wait to finally wear that famous black and white shirt.
"I've always watched the BaaBaas with such affection because of their style and how the team approaches the game.
"I feel like the Barbarians and myself could be a match made in heaven, so I really can't wait to throw my own bit of flair into an already incredible team."
England internationals Ben Youngs, Zach Mercer and Jonathan Joseph have already been chosen by the Barbarians for the Fiji match, which forms part of a Twickenham 'double-header' with world champions South Africa facing Wales at English rugby union's headquarters earlier on the same day.
Matches involving the Barbarians, a multi-national side with a tradition of including at least one uncapped player in their starting side, are generally not regarded as full Tests but rather non-cap internationals.
The Barbarians' most celebrated match was a 23-11 win over New Zealand in Cardiff in 1973, a game that featured what many pundits still regard as the greatest try in rugby union history when outstanding Wales scrum-half Gareth Edwards dived in at the left corner to cap a length-of-the field move in the opening few minutes.
