Bill Ackman is planning to take his investment firm public as soon as next year, the boldest move yet by the hedge-fund manager to capitalise on his social-media fame.

As a precursor to a public listing, Ackman is selling a stake in the firm, Pershing Square, to investors in a funding round expected to value the firm at about $10.5bn, people familiar with the matter said. That deal is expected to close in the coming days.