A chemical giant that’s under pressure from activist investor Bill Ackman has decided to split itself into two separate companies, The Post has learned.

Platform Specialty Products is expected to announce Thursday that it will pursue a public offering of its agricultural pesticides division, according to sources briefed on the situation.

In the process, the company is nixing an auction of the agricultural unit, which had drawn interest from prospective bidders including billionaire Stephen Schwarzman’s Blackstone Group, sources said.

Platform Specialty Chairman Martin Franklin and Ackman mutually agreed to scrap the auction process for the unit, whose manufacture of products to protect berries, grapes and beehives represents about half the overall business, a source said.

Ackman’s hedge fund Pershing Square Capital is the leading shareholder, with a 14.5 percent stake.

Last month, The Post reported that Blackstone had advanced in an auction that valued Platform’s agricultural division at more than $4 billion.

Platform Specialty declined comment.