The signing joins last week's new boy Willo Flood at Pittodrie, and is the next piece in McInnes's jigsaw after the new gaffer persuaded Niall McGinn and Josh Magennis to pen new deals.
Robson will join up with Flood yet again, after playing with him at Dundee Utd, Celtic and Middlesbrough, and like Flood will officially join the Dons when his current contract expires.
Robson has 17 caps for the national team, and in a move that is remarkably similar to recently departed midfielder Gavin Rae is a local lad who has only just got round to playing for the Dons in the twilight of his career.
McInnes told RedWeb: "Barry is a player I know well and having been a teammate of his I can see the same hunger and determination within him as he had when I played alongside him. It's clear to see he has retained a high level of performance.
"Both Tony and I have watched him recently and have only had good reports about his performances for Sheffield United.
"We still feel he has that winning mentality and is someone who can bring some real quality to the team.
"We're delighted to have him on board and as a local boy I'm sure he is looking forward to playing for his home town team."
Listen to what Robson had to say in an interview with RedTV here
Source: Aberdeen Mad