Sullivan & Cromwell is advising SoftBank Group on the planned NASDAQ IPO of its UK subsidiary, chip designer Arm Holdings, which is represented by Morrison & Foerster. Davis Polk & Wardwell is acting for underwriters.

Reuters reported that SoftBank was planning to sell about 10 percent of Arm's shares in the IPO and seek a valuation of between $60 billion and $70 billion for the chip designer, making it the largest listing of the year globally.

It added that the stock market launch is expected to bring back to life a lacklustre IPO market, which has seen many high-profile startups put off their listing plans over the last year due to market volatility.

MoFo has been a long-standing advisor for Softbank. Earlier this year, the firm advised the Japanese conglomerate on the sale of a majority stake in U.S. asset manager Fortress Investment Group to Mubadala Investment in a deal estimated at around $3 billion.