Brown's deal sees the 21-year-old join the squad's existing drivers David Reynolds and Anton De Pasquale, who have both agreed new multi-year deals with the team this year.
He will also partner Reynolds, who penned a 10-year contract with Erebus this year, in next year's Pirtek Enduro Cup.
Signing Brown is a bold move but one that ensures the team has a steady stream of talent for the future.
While Brown is ready to slip into De Pasquale's seat should he move, Ryan is hopeful the team will retain all of its drivers to run a three car attack in 2021.
Such a move would require the Melbourne team to acquire a third Racing Entitlements Contract.
“All we are trying to do is make sure in the years to come we can win a championship,” Ryan told Speedcafe.com.
“It is simple to say that Dave can win a championship, which he probably can, but we need to know if he can't we have got Anton there or Will there.
“We want to win the championship and that is all we are focused on.
“You can't do it without having stability in the team so we are trying to create stability.
“If Anton stays and we sign him up for five years and if Will stays along with Dave, we will have three top line drivers who are all going to give us chances to win championships and win Bathurst.
“It is a big thing to chew but we have got to make sure that commercially we make it sustainable.
“We are comfortable we can, so we have to make these decisions and run with them.”
This season, Brown enjoyed an active campaign where he dovetailed a Super2 season with a title winning run in TCR Australia, and outings in S5000.
Ryan has confirmed that Brown's new deal will not preclude him from racing in other series, with Brown expected to return to defend his TCR crown next year.
“We will be very flexible next year. He is still going to do TCR and hopefully S5000,” Ryan added.
“He is still only a 21-year-old guy so he needs as many miles as he can get.
“We will back him on doing whatever he can. We will make sure he is doing the right stuff so it won't hamper what he is trying to do in the main game.”