Brown's return to New Zealand was confirmed on Monday, with the current Springbok attack coach signing a two-year deal.
However, his arrival has created an unusual timing situation, as the current All Blacks coaching group led by Dave Rennie is only contracted through the end of the 2027 Rugby World Cup in Australia.
That means Brown has effectively been lined up for a role beginning in 2028, even though there is still uncertainty over who will be in charge of the national team following next year's World Cup.
Despite that, NZ Rugby has moved to lock in Brown's services early, ahead of any post-2027 reshuffle in the coaching setup.
"We've got a world-class coach, an acknowledged world-class coach who's highly sought after in Tony Brown," Lancaster told Sky Sport. "We had the opportunity to secure him, and we've taken that opportunity. It's that simple."
Lancaster made it clear that current head coach Rennie was fully involved in discussions around Brown's appointment, and also moved to dismiss any suggestion that Brown's arrival would create tension with recently appointed attack coach Mike Blair.
"It doesn't have any bearing on Dave or his group," he said. "Dave's been fully engaged in the process and fully supportive of securing Tony.
"Let's hope Dave is still the head coach beyond 2027 and sees a place for Tony in his group."
On potentially having two attack coaches on the books, Lancaster said they don't see this as a "one-in, one-out situation".
"Tony adds value to whichever coaching group he comes into.
"It's about having the right people in the mix. We've got the right person on the bus, and we'll work out what seat he sits in later."