Jackson, 32, boasts a professional record of 27 wins, 12 by knockout, 11 losses and four draws.
In 2014 he took on four-time world champion and former State of Origin rugby league star Anthony Mundine and lost by a unanimous points decision.
The vacant Universal Boxing Federation's Asia Pacific and New Zealand Professional Boxing Association's middleweight titles will be up for grabs.
O'Brien's Napier Boxing Club clubmate and fellow professional Toa Leutele will fight Wellingtonian Cory Enoka for the vacant heavyweight titles from the same two organisations.
"I was mentally preparing for Gunnar. If I could have anyone as a replacement fighter it would be him," O'Brien said.
He agreed the advantage of fighting such a well-known opponent is the fact there is no shortage of footage.
"There isn't going to be a stoppage. I'm going to have to fight hard and fast and try and be technical. There's no point trying to lure him into traps as he has probably written half the traps out there.
"Fitness isn't going to be an issue I'm training five times a day ... it's going to be an awesome show for the Hawke's Bay fans," O'Brien said.
"Obviously this fight will be a huge step up for me. But I will still be doing everything to try to get the win and if I can it will open up so many potential fights for me particularly on the American circuit," O'Brien explained.
"I'm excited about it and I love being the underdog. I'm more excited about this one than the one in Fiji back in June," he added.
O'Brien was referring to his fifth-round TKO against previously unbeaten Fijian Silevini Nawai for the World Boxing Foundation Australasian middleweight belt.
That took O'Brien's professional record to six wins, a draw and a loss.
Thomson is rapt to have secured Jackson.
"It took a fair bit of negotiating and I had to dig a little bit deeper into my pocket but you have to do that to get the best boxer and I'm sure it will be worth it."
"Gunnar has never been on the canvas and is to his weight division what Joe Parker is to his," Thomson said.
Leutele, 24, will be having his first fight since winning an eight-man heavyweight eliminator competition in Melbourne in July. Thomson said Enoka has moved up to the heavyweight ranks after winning multiple national cruiserweight titles.
Should Leutele beat Enoka, he will have the opportunity to fight Aucklander Junior Fa for the New Zealand heavyweight title.
Parker, Shane Cameron, David Tua and Sonny Bill Williams are among the fighters who have held this national title.
In addition to the two professional bouts, nine corporate fights scheduled for three two-minute rounds involving Hawke's Bay fighters as well as boxers from throughout the lower North Island will be staged.
Thomson pointed out these corporate fighters are regular boxers, unlike those who train for charity bouts.
"They don't want to be amateurs but they don't consider themselves ready to go professional but fight regularly."
Tickets for the event are available from Ticketek and fans wanting to reserve ringside tables are to contact promoter Scotty Thomson on 021 190 0995.
THE CARD
Katie Hatton (Napier Boxing) v Orewia Spooner (Gisborne); Ripeka Dwyer (Highlander Boxing, Napier) v Rebecca Forrest (Wellington); Junior Alivale (Highlander Boxing, Napier) v Charlie Rudd (Kapiti Boxing, Wellington); Nina Houston (Napier Boxing) v Stacey Loye (The Lab, Napier); Dom Leiataua (Highlander Boxing, Napier) v Tabai Tumanako (Lion Pitt, Wellington); Tommy Harrison (Napier Boxing) v Gerhard Van Vuuren (Wellington); Jimmy Pentland (The Lab, Napier) v Callum Aldiss (Wellington); Cody Thomson (Highlander Boxing, Napier) v TBC; Elliot Sharp (Kapiti Boxing, Wellington) v TBC; Toa Leutele (Napier Boxing) v Cory Enoka (Bellview Boxing, Wellington); Beau O'Brien (Napier Boxing) v Gunnar Jackson (Tauranga).
