Homelessness charity Emmaus was forced to close all three of its shops in the city after one of its volunteers tested positive on July 29.
Staff and volunteers were forced to self-isolate for two weeks whilst collections and deliveries were also suspended.
The charity said its latest batch of test results had come back negative, with no other cases of coronavirus detected among those working at its stores or living at its residential shelter in the city.
Emmaus has three stores in Preston - a charity shop in Fishergate, its Megastore in the former B&Q in Brookfield Street and a superstore off Ribbleton Lane in Deepdale.
Its Fishergate shop and its Megastore in Brookfield Street will reopen tomorrow (Thursday, July 12), and van collections and deliveries will also resume.
A spokesman for Emmaus said: "We are happy to report that the Emmaus Preston Megastore and Fishergate Charity Store will reopen tomorrow.
"Thankfully, all COVID-19 tests for our companions and staff have now come back negative and nobody is experiencing any COVID-19 symptoms or showing any signs of illness.
"So, all being well, we are planning to reopen the Emmaus Preston Megastore and Fishergate Charity Store on Thursday, August 13.
"We'll have our full range of COVID-19 safety measures in place, lots of great value items and our usual friendly service.
"We really do appreciate everyone’s support in Preston."
Emmaus is home to a community of formerly homeless people who live together within communal sheltered accommodation in Preston. Members of the community, known as 'companions' often work in its shops whilst receiving support and training.
The charity said all of its 'companions' and staff had recently been tested and no further cases detected. It said strict hygiene measures will continue in-store and shoppers are being asked to wear face coverings at all times.
An Emmaus spokesman added: "Our stores will reopen with the same wide range of COVID-19 safety measures including regular cleaning of stores, one-way systems, customer sanitiser stations, card payments only and face masks.
"If you’re planning on visiting us, please remember to bring and wear a face covering at all times and sanitise your hands on entry.
"In line with the recent guideline changes for Preston, we ask that you visit us on your own, with members of your household or social bubble.
"If you are showing any coronavirus symptoms or feel unwell in any way, please do not visit our charity stores.
"We have a wide range of brand new and fresh donated goods sat waiting for a new home. If you're in need of some items, please come for a relaxing shop and give your support to Emmaus Preston.