Knowsley Housing Trust is to spend £57m building 570 homes in the next three years, half of them in the next 12 months. There will be 319 affordable rent units in the programme.
Just 37% of the homes in Knowsley, which has a population of 145,900, are classed affordable by national charity Shelter.
The new affordable properties will span seven sites in Huyton, Kirkby, Halewood and Prescot. There will be a mix of one- and two-bed apartments, two- and three-bed houses and several one-bed apartments.
The new stock from KHT will include 251 homes for sale through a mixture of shared ownership and outright sale.
The plans also include the extra care housing development at Bluebell Park, Huyton, which comprises 122 apartments for residents aged 55 and over.
Ian Thomson, executive director of KHT, said: "New homes in Knowsley are in demand, and it's important that we act responsibly to plan and recognise the needs of our community.
"Our vision is to develop high quality yet affordable homes which provide future homeowners and residents with a wide variety of options, to ensure they can select the property which works best for them, all while keeping money in their pockets. As a responsible landlord and developer, every project we develop is designed to inspire communities and support the region's residents.
"We're continually pushing for further development across the North West and are working with some of the UK's most renowned contractors to deliver quality, affordable homes and our objectives. As an organisation, we have an extremely strong infrastructure and reliable team in place to deliver each of our projects to the highest possible standards."