The new dualled section of the A421 and the enlarged Kingston roundabout will improve journeys and help develop 2,900 new homes.
The works received Department for Transport (DfT) funding through the Local Pinch Point Fund (LPPF) programme, with the government providing £9m of the total £17.4m cost.
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Minister Jones said: "Better roads help people get around and get on, as well as bringing long-term benefits to local communities. The project improves an important route to Milton Keynes from the M1 and continues the government's investment in transforming the UK's road network."
The £263m LPPF was launched in 2013 and is aimed at reducing congestion and helping local authorities make upgrades to vital roads and junctions.
Additional funding from developers and other supporters means there is up to £500m of funding available.
(LM/CD)
