Founded in Cincinnati, Ohio, in 1885, the NSX was due to close at the end of this week.
But NYSE owner Intercontinental Exchange (ICE) announced it has agreed a takeover, with the deal expected to complete in the first quarter of next year.
The deal, which is subject to approval from the Securities and Exchange Commission (SEC), will see NSX continuing to operate beyond this week.
The acquisition will bring the NYSE Group an additional US exchange licence, taking its total to four.
Earlier this year, ICE pulled out of plans to bid for the London Stock Exchange and disrupt its merger with Germany’s Deutsche Boerse.