The deal will involve JPJ paying £250m in cash and £240m in shares, excluding Gamesys' sports brands and games, and will see JPJ rename itself Gamesys Group PLC.
JPJ has previously done business with Gamesys, having sold Jackpotjoy to Intertain Group Ltd in April 2015.
Gamesys shareholders will own 31% of the new group.
Gamesys CEO, Lee Fenton, will become the CEO of Gamesys Group PLC, while JPJ’s Executive Chair Neil Goulden and CFO Keith Laslop will remain in their respective roles.
JPJ reported its shares were 5% higher on Thursday morning at £8.08 each.
Goulden said: “This acquisition marks an important transformational step in JPJ’s growth, providing significant benefits for shareholders, employees and customers.
“For shareholders, we expect the acquisition to deliver earning accretion in the first full financial year of ownership.”
