The former Manchester United and Scotland international will be unveiled formally at a press conference this afternoon at The Riverside.
The 52-year-old Strachan left Celtic at the end of last season, and will be asked by Boro chairman Steve Gibson to spearhead the club's return to the Premier League.
Southgate was sacked following Boro's 2-0 victory against Derby County on Tuesday, with his side lying fourth in the Championship.
It has since transpired that the Boro chairman made the decision at the end of September, following a 1-0 defeat to Leicester City.
- Football.co.uk staff
Source: DSG
