The development work, funded by Welsh Government and Cardiff Council, will widen the walk and cycle way to seven meters. This will enhance the path and improve usability for up to 150,000 people who cross the Barrage every month.
Cabinet Member for Culture and Leisure, Cllr Peter Bradbury said: "The decision to expand the Bay walkway comes in response to feedback to improve the pathway, which forms part of the Wales Coast Path and Bay Trail.
"Unfortunately, there can be no public access whilst the work is carried out for safety reasons. Access to the site will only be available to contractors. Hopefully, giving a month's notice of the works will give all users of the walkway enough time to plan alternative routes. The skate park and play area will remain open, accessible from the Penarth side of the Barrage.
"These improvements will also provide visitors with easier access to the leisure attractions along Cardiff Bay Barrage, as well as the event site for the Volvo Ocean Race, which stops in Cardiff in May 2018 for two weeks."