Mayhoola for Investments, an investment vehicle with close ties to Sheikha Mozah, the second wife of Qatar's former emir, has asked Rothschild to involve a number of banks in the listing, which could happen as soon as May, the sources said.
Valentino and Rothschild declined to comment. No one at Mayhoola was immediately available to comment.
For the luxury label, once worn by Jacqueline Kennedy Onassis, Audrey Hepburn and Elizabeth Taylor, it will mean a return to the Milan stock market having been bought out by private equity firm Permira in 2007.
In addition Valentino's listing is expected to pave the way for other fashion floats to follow, with Versace, backed by US buyout fund Blackstone, likely to go down the same IPO route in around 18 months, several sources familiar with the matter said.
Valentino's timetable will largely depend on market conditions, another source said, but Mayhoola will try to take advantage of the first available window in the second or third quarter of 2016.
The sources ruled out Versace jumping the queue on an IPO before its bigger rival Valentino returns to the Milan market next year.
Led by Chief Executive Stefano Sassi, Valentino expects to generate revenue of 1 billion euros ($1.09 billion) in 2016 with earnings before interest, tax, depreciation and amortisation (EBITDA) of close to 200 million euros, two of the sources said.
It will compete on share price valuations with several other Italian fashion companies, including Moncler and Ferragamo, which trade on a multiple of more than 10 times their expected EBITDA, while Brunello Cucinelli trades on a multiple of over 14.
The sources said the Milan bourse remains the main marketplace for fashion firms and ruled out Mayhoola seeking a listing for Valentino in New York or in Hong Kong, where Italian rival Prada was floated in 2011. Founded in 1960 by designer Valentino Garavani, the Italian brand became famous for its trademark bright-red chiffon dresses.
Permira took control in 2007, paying 5.3 billion euros at a time when sector valuations turned out to be at their peak.