The new facility was officially opened by HM Lord-Lieutenant of Northamptonshire James Saunders Watson at a ribbon-cutting ceremony on Friday, August 14.
Located alongside the hospital's existing Emergency Department, the Urgent Treatment Centre (UTC) will replace the previous Springfield Urgent Treatment Centre and create a new "front door" for urgent and emergency care at NGH.
Patients arriving at the centre will be assessed before being directed to the most appropriate care pathway, which could include urgent treatment, emergency care or specialist paediatric services.
The hospital says bringing services together in a new central hub will support faster assessments and clearer patient pathways, while helping Emergency Department teams concentrate on patients with the most serious and life-threatening conditions.
Services will move into the new building in phases over the coming weeks while final commissioning and operational preparations are completed.
Polly Grimmett, director of strategy, said: "This investment represents an important step forward for healthcare in Northamptonshire and demonstrates our commitment to providing high-quality care for the communities we serve.
"The new Urgent Treatment Centre provides modern facilities for patients and staff and supports our ambition to deliver excellent care in an environment designed around the needs of those who use it.
"As demand for NHS services continues to grow, investments such as this are vital to ensuring local people can access the care they need, when they need it."
Sarah Noonan, chief operating officer, said bringing urgent and emergency services together would improve patients' experience and how people move through different care pathways.
She added that the phased opening would allow the hospital to make the transition "safely and smoothly".
Minister of State for Health Dame Diana Johnson said patients and NHS staff in Northamptonshire "deserve modern facilities that are safe, efficient, and fit for the future".
She said: "This new £15.75 million Urgent Treatment Centre at Northampton General Hospital will help patients access the right care more quickly, while supporting staff to deliver urgent and emergency care in a modern environment designed around the needs of local people."
The NHS has stressed that the new centre does not change how people should access urgent care.
People with an urgent healthcare need which is not life-threatening are encouraged to use NHS 111 online or call 111 before travelling to hospital.
NHS 111 can assess symptoms and direct patients to services including community pharmacies, GPs, urgent treatment centres or the Emergency Department where necessary.
13. The new £15.75 million Urgent Treatment Centre has been completed at Northampton General Hospital
The new £15.75 million Urgent Treatment Centre has been completed at Northampton General Hospital Photo: Kirsty Edmonds