Tradeweb Markets Inc., the bond and derivative platform co-owned by financial-data platform Refinitiv, filed for a U.S. initial public offering, kicking off plans to go public five months after being acquired as part of a $17 billion buyout.

Tradeweb filed with an initial offering size of $100 million, typically a placeholder amount used to calculate fees that’s likely to change. The IPO is being led by JPMorgan Chase & Co., Citigroup Inc., Goldman Sachs Group Inc. and Morgan Stanley, according to a filing with the U.S. Securities & Exchange Commission Thursday.

Net income at Tradeweb in 2018 was $159.5 million...