Public consultation this year saw 95% of people back a council concept for a space with more trees, grass and other greenery.
A detailed design has since been drawn up which has been presented to the cabinet.
Members agreed to commit capital finance funds to support the development over the next two years.
The plans will now go through a formal planning process next summer.
If plans are approved, the new gardens could be in use by late 2023. The upgrade forms part of Swansea' £1bn regeneration, linking in with the new-look Kingsway and Wind Street, with Copr Bay and with other forthcoming multi-million pound schemes in locations such as the Civic Centre site.
Together, they will see thousands of jobs retained and created in the city centre and Swansea become a place where more people want to live, work, study and spend quality free time.
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The latest plans for Castle Square Gardens show:
More greenery: A planting scheme has been developed to incorporate new trees, green roofs, raingardens, and more accessible landscaped areas. It will reflect the council's green infrastructure strategy. Biodiversity would increase and existing trees would remain, with new trees planted.
Two café-restaurant pavilions: One will be in the current stepped area, the other near the Zara shop.
A more active area: The current water feature will go. Instead, there will be water jet features at ground level.
A stronger identity: Central to the design is a highly patterned floor using existing stone plus new granite insets. Modern lighting and digital art features are also planned.
Improved connections with neighbouring areas:New seating and outdoor dining areas could be introduced in Temple Street and Princess Way.
The vision, which takes into account public opinions expressed to the council over the past few years, has been drawn up by respected architects ACME and development managers Spider.
Council leader Rob Stewartsaid: "Our greener, more welcoming Castle Square Gardens will play a key role in Swansea's big future. This 21st Century concept has a keen eye on the location's green past.
"People will want to spend more time in Castle Square Gardens, host events there and enjoy its more active, distinctive look.
"It will be much more family friendly - a Castle Square Gardens for the 21st Century."
