The Shropshire Council project, which focuses on the middle level of the Darwin Centre, will see brand new toilet facilities, a new family room and a changing facility, plus new flooring, wayfinding signage and shop fronts on some units.
The existing ceiling will be stripped out and new lighting installed to make the centre brighter and lighter.
Shrewsbury shopping centres manager Kevin Lockwood said: "This work will make a huge difference to the Darwin Centre and make the middle level a much nicer and more appealing place to visit, shop and work.
"Once the work is finished people really will see a huge difference. The toilets, family room and changing places facility will be something that the whole town can be proud of, and the new flooring, lighting, shop fronts and signage will make a really positive difference to the centre, our customers and our tenants.
"We apologise for any inconvenience people may experience during this work, but any disruption will be kept to a minimum, and we encourage people to continue to visit the centre and our shops in the coming weeks."
Work, which will be carried out by John Graham Construction, is due to start on March 9 and end this summer.
To minimise disruption, most of the work will be carried out overnight and in three phases.
The existing toilets will be closed from March 9, and signage will be put in place to advise people of the nearest alternative facilities.
Steve Charmley, Shropshire Council’s Cabinet member for assets, economic growth and regeneration, said: "This work is a significant investment in Shrewsbury’s primary shopping centre, and something that we’re sure will attract people to the centre from Shrewsbury, Shropshire and beyond – benefitting the economy of the town and the county.
"Of course, a newly-refurbished centre will also help us to retain our existing tenants and attract new ones, as it will be much nicer place to work and run a business.
"The refurbishment of the centre was begun by the previous owners and when we bought the centres we committed to finishing this important work. I’m really pleased that work will soon be underway."
Shropshire Council took the decision to purchase Shrewsbury’s three main shopping centres for £51 million in December 2017.