Orion's offer was immediately recommended by the Cassell board and accepted by holders of 50 per cent of the shares. The bid trumps Macmillan's offer of 100p and values Cassell at pounds 9.2m.
Orion is paying nearly three times the market price of Cassell's shares on 9 October, the last trading day before Macmillan made its bid, when they traded at just 45p.
Philip Sturrock, the chairman of Cassell, admitted yesterday that Cassell's sales last month were worse than expected and October sales continued to be disappointing.
But he said: "Orion's offer more accurately reflects the value of Cassell's unsolicited bid. I believe that Cassell will benefit from being part of this new vibrant group."
Orion includes Phoenix and Weidenfeld & Nicholson, and among its authors are Ian Rankin, Maeve Binchy, Stephen King, Vikram Seth, Antonia Fraser and Edna O'Brien.