The branch, in the Co-op store in Arundel Drive, was officially opened yesterday, and will be open seven days a week between 6am and 10pm.
In addition to posting mail, customers can benefit from services including collecting and returning online shopping items, bill payments and foreign currency exchange.
Banking services are also available, including cash withdrawals and balance enquiries for customers of all the main UK banks.
The new branch joins other local branches in Funtley, West Street and Hill Park.
Daniel Rooney, Post Office multiples account executive, said: ‘We want to make it as easy as possible for customers to pay their bills, withdraw cash from their bank accounts, and send and collect their mail at a time and place that suits them best. We know how important our services are to customers and are confident that this brand new Post Office, alongside the other branches in the area, will ensure that people in Fareham have easy access to our services.’