The Barnsley defender has been the subject of transfer speculations following an outstanding time in the Championship last season.
Swansea City and Huddersfield were the frontrunners in the chase for the 25-year-old amid Barnsley’s efforts to hold on to their man, but it appears The Terriersare going to have the last laugh.
The Tykes initially rejected separate bids from Swansea and Huddersfield for the Ghanaian, with manager Paul Heckingbottom describing the latter’s £750,000 offer as "disrespectful".
Swansea reportedly put in a second bid worth £3 million but it is the new boys who now look set to snap up the London-born after agreeing terms with Barnsley.
Yiadom will become coach David Wagner’s 11th signing of the summer as they kick off the Premier League campaign at Crystal Palace on Saturday.
The utility man has already made two appearances for Barnsley this season, adding to his 32 league outings last campaign.
He was in action as the Tykes succumbed to a 3-1 defeat to Bristol City in the Championship opener on Saturday, before seeing another full-time action in their 4-3 League Cup win over Morecambe on Wednesday night.
Yiadom joined Barnsley from Barnet in summer last year, having also played for Braintree Town and Hayes &Yeading FC.