The facility will be based under the markets canopy, close to Lancaster Road.
Both of the units are designed to identify so-called "asymptomatic" cases of coronavirus and help stop the spread in the city.
The Lancaster Road facility will be open between 10am and 3pm, Monday to Saturday, excluding bank holidays. No appointment is necessary, but those attending should wear a mask.
Anybody with Covid symptoms should call 119 to book a test at the regional drive-through testing base at Preston's College. People requiring a result within 48 hours hours should also use this option, as the results of tests taken at the two community units can take up to seven days to come through.
Cllr Matthew Brown, leader of Preston City Council, said: “This new site in the heart of the city will help residents from across Preston get a quick and painless test for coronavirus.
“With cases on the rise across the region, it’s vital as many of us as possible get tested for the virus and for everyone who receives positive results to self-isolate. This is an important way for us to stop the spread of the virus.
“We need everyone’s help. In order to demonstrate a low percentage of positive tests, we need more people to be tested. And in order to achieve that low percentage, we need everyone to continue to follow government guidance and take the restrictions seriously.”
Preston Markets – including the outdoor market – will continue to operate as normal.