The U.S. investment bank would pay 25 million ($39.1 million) pounds for the stake in the world's largest metal market, the sources said, implying a total value of around 530 million pounds for the operator.
An announcement could come as early as this week.
The sale to J.P. Morgan could shift the odds in the takeover battle for the LME, one of the few exchanges to still operate an open outcry ring, which has thrown its doors open to a potential 1 billion pound takeover.
J.P. Morgan, which already holds a 6.2 percent in the LME, declined to comment. The LME also declined to comment, as did KPMG, the administrators for MF Global's UK unit.
J.P. Morgan would separately also buy the B-shares held by MF Global for 2 million pounds, one of the sources said.
Industry sources told Reuters last Wednesday that MF Global's ring dealing seat on the LME will be bought by U.S.-based broker INTL FCStone.
Selling the stake would be a boost for creditors of the futures brokerage, which filed for bankruptcy protection last month, and for its clients, some of whom have seen their positions frozen ever since.