‘Grow or Die’ Drives 110-Year Old Chicago Broker to StoneX Sale

R.J. O’Brien & Associates started life in late 1914 as John V. McCarthy & Co. to sell butter and eggs on a cart through the streets of Chicago. Over the next century, the firm expanded to broker and clear a dizzying array of futures and financial instruments from London to Dubai to Singapore.

Now, the family that controls R.J. O’Brien has agreed to sell it to New York-based StoneX Group Inc., a fast-growing financial services firm, for $900 million. The deal closes a chapter on one of the last surviving founding members of the Chicago Mercantile Exchange.

“My father ...