Wolves are holding a press conference at their Compton training ground to announce the signing of the former Cardiff player - barring any last-minute hitches.
The clubs have agreed a fee while Johnson has agreed personal terms and passed a medical. All that remains is for Johnson to formally put pen to paper on a four-year contract ahead of facing the media.
Wolves manager Mick McCarthy has been tracking Johnson since the end of season when Birmingham's relegation from the Barclays Premier League was confirmed.
He is an admirer of his committed and never-say-die approach to matches - qualities often endorsed by the then Blues manager Alex McLeish.
Johnson has also made it clear he wants to remain in the top flight.
He moved from Cardiff to St Andrew's during the summer of 2009 in a £5million deal.
Johnson - a lifelong Chelsea fan - formed an effective partnership with Scott Dann during his two years at Birmingham.
McCarthy will want Johnson to shore up a defence which was guilty of leaking too many soft goals last season and left them needing to avoid relegation on the final day of the season.
The Wolves boss has now spent nearly £12million this summer, with midfielder Jamie O'Hara also moving from Tottenham in a £5million deal. Keeper Dorus de Vries moved to Molineux from Swansea on a Bosman transfer.
Source: PA
Source: PA