City Quays 4 is a proposed 256-apartment build-to-rent development that is part of the overall City Quays masterplan. City Quays 4 will be located next to the AC Mariott Hotel which was also built as part of the City Quays masterplan. City Quays 4 is expected to be around the same size as City Quays 3.

In July 2020, Belfast Harbour said it was still looking at a co-developer for its buy-to-let City Quays 4 project, but had gone through some setbacks due to the Covid-19 pandemic and as a result, may be delayed.

In June 2022, Belfast Harbour revealed that its financial performance bounced back in 2021 as port activities recovered to pre-Covid levels. They said that they were now in pre-application discussions about two further phases to City Quays which will include City Quays 4 - a 260-unit build-to-rent residential development and hinted towards progress on the development of City Quays 5. A planning application is expected to be submitted towards the end of 2022.

In September 2022, a Proposal of Application Notice was submitted for City Quays 4 (LA04/2022/1752/PAN) which comprises a residential apartment development comprising circa. 270 residential units, landscaping and associated site works.

In October 2022, the online consultation of City Quays 4 went live. The consultation revealed plans for 270 homes, comprising of a mix of studio, one & two-bedroom homes, public and private communal spaces, co-working space, a gym and 24-hour Concierge Services. The consultation also revealed that City Quays 4 will be designed for the build-to-rent market and will offer rent-only apartments that are managed by an operator.

In December 2022, Belfast Harbour Commissioners submitted a planning application (LA04/2023/2388/F) for City Quays 4 proposing a residential development comprising 256 no. units, public realm, and associated access and site works.

In January 2024, City Quays 4 was recommended for approval at the Belfast City Council Planning Committee.