Simon has offered 424p per share via acquisition vehicle Drillgreat, for the 24.5% of the company he and his family does not own.
Monsoon's board has recommended the offer to shareholders and US hedge fund Polygon Global Opportunities Masters Fund, which holds around 2.3% of Monsoon has also indicated it will support Simon's offer. Polygon's support means Simon's bid is likely to succeed.
Simon's approach has been long awaited by the City and comes after months of speculation Simon was planning to take the company private. He is known to dislike the scrutiny of being a public company and has been criticised by analysts for his unconventional approach to running the business.
Monsoon has not had a chief executive since Rose Foster quit to join La Senza earlier this year. Former House of Fraser deputy chief executive David Adams was offered the job but is understood to have walked away when he realised the position would not have a seat on the board.
Monsoon issued a profit warning earlier this year blaming problems at its new distribution centre, increased competition against its Accessorize chain and the wash out spring season. At its AGM today the retailer said that sales for the 17 weeks to September 22 had fallen 2%, with like-for-likes down 9%.
Simon said in a statement: "Trading since the start of the new financial year on 27th May 2007 has continued to be very poor, as indicated in our preliminary results in July when we stated we were facing 'a deteriorating economic environment and rising interest rates. Total sales for the first 17 weeks of the financial year to 22nd September were 2% down, with like-for-like sales down 9%, compared to 6% down last year. Both UK and International sales were equally affected and suffered similar like-for-like declines."
Monsoon's shares closed at 407.5p yesterday.