O’Neill, in charge during the highs of Cougarmania in the 1990s, is the new chairman after a deal was concluded to buy the League 1 outfit who had been in special measures under previous owners Austria Holdings.
The Rugby Football League Board has approved the transfer of membership although Keighley have accepted they will start the new season – at Whitehaven on Sunday February 17 – with a 12-point deduction.
However, head coach Craig Lingard – who resigned in November for three weeks in protest to unpaid wages for his squad and staff – can now start signing players again.
O’Neill, who moved to Australia after his first spell, said: “Being back in control after 20 years means so much to me personally and my family.
“The town desperately needs a successful rugby league club and we intend to make that happen.
“All the directors feel the same. We are all looking forward to the challenge and will be working hard to bring a smile back to Cougars and the game.”
He has been joined by Mike Smith and Tim Wood, who were also involved when they won the second division but were denied a place in Super League in 1995.
Other directors are O’Neill’s son Ryan and his husband Kaue Garcia, who run a children’s technology company, plus Keighley-born Mike Loughtman, who resides in Sydney.
Ownership is split evenly, a voluntarily allocation of 10 per cent of the shares has been given to the Cougars supporters club while Gary Murgatroyd is the club’s new general manager.
Austria Holdings, represented by Shane Spencer, took over in August but financial problems soon emerged and numerous players left for other clubs.
Keighley stay at Cougar Park and O’Neill added: “We have to thank the RFL for the enormous support they have given us during negotiations with the previous owner and accepting our application to run the club at the end of a very difficult period for all concerned.”