Paper Plus assistant manager Rachel Brock said the existing services at the site were well supported.
"We expect that the customers who currently use the Victoria Ave branch will find it convenient to come here," she said.
Parker said the move was good news for Paper Plus Whanganui.
"This model of working with local businesses is very successful for NZ Post and our customers.
"It's also good for the local businesses we work with as they enjoy additional income, both from transacting postal services on our behalf and by having more customers coming through their doors."
Parker said NZ Post was "not expecting any changes at any other postal services outlets in Whanganui at this time".
The post office box and private bag facilities will remain in place at Victoria Ave.
The commercial lead of Whanganui and Partners economic development agency, Rhonda Morris, backed the move as positive.
"Trafalgar Square is very much part of the CBD and it has good access and parking," she said.
"It is a hub where people can do shopping and pay bills under one roof.
"Some people may not like the change but I think once they get used to it, they will find it convenient."
Meanwhile Kiwibank, which shares the Victoria Ave store with NZ Post, will stay put.
Kiwibank communications manager Kara Tait said the Victoria Ave branch would continue to operate from 9am until 4.30pm, Monday to Friday.
"We've had great feedback from customers on the standalone branches we've opened across the country and we're excited to bring an environment that supports specialised banking conversations to Whanganui."
New Zealand Post services are also available at Lindsays Lotto Post & More, 67 Moana St, Whanganui East; Aramoho Mags & Lotto, 140 Somme Parade, Aramoho; Gonville Post + More, 51 Abbot Street, Gonville, Four Square Castlecliff, 2 Bryce St, St Johns Four Square, 15 Great North Rd, St Johns Hill; and parcels can also be posted at Whanganui Courier Post Depot, 62 Wilson St.
