Joshua, who holds the WBA and IBF versions of the title, will add Parker’s WBO belt if he triumphs at the Principality Stadium, leaving only American WBC champion Deontay Wilder on his title hit-list.
The announcement brings an end to months of fractious negotiations with Parker, who defended his crown with a points win over Hughie Fury in Manchester in September and was holding out for a bigger percentage of the purse.
It will be Joshua’s first fight since a gruelling late stoppage win over 11th-hour replacement Carlos Takam at the same venue in October and a win will move him closer to his goal of being the first heavyweight to hold all four major belts simultaneously.
Joshua said: “It is a unification heavyweight championship fight. We all know what happened last time I was in a unification heavyweight championship fight – it was gruelling, it was interesting and we both left the ring with masses of respect.
“These fights aren’t easy because there is a lot on the line, so respect to team Parker for taking the challenge. I am looking forward to it, training camp is under way and before you know it March 31 will be upon us.”
Parker, who has won 18 of his 24 professional bouts inside the distance, is the natural next step for Joshua despite his underwhelming performance against the back-pedalling Fury, when he escaped with a majority decision.The 26-year-old claimed the WBO crown by beating Andy Ruiz Jr in Auckland in December 2016 and made a low-key defence against Razvan Cojanu before venturing out of the southern hemisphere for only the fourth time to face Fury.
It was this relatively low-key career – in stark contrast to Joshua’s stadium-filling capabilities against the likes of Wladimir Klitschko – which prompted the disparity in expectations between the two parties.
The problem for Joshua’s camp was the lack of obvious alternatives, with a deal with Wilder still some distance away and former champion Tyson Fury still yet to return.
Parker clearly believes Joshua may be underestimating him, insisting: “Anthony Joshua is in for a huge shock.”