The new 24km scheme will form part of the southern section of the inter-urban corridor from Waterford to the capital.
It will run from Knocktopher in Co Kilkenny to the N25 Waterford city bypass, which is currently under construction.
At a sod-turning ceremony in Mullinavat, the minister announced Ascon Ltd had been awarded the contract.
The project, he said, was one of seven national road schemes to commence this year under the Government’s investment programme, Transport 21.
The entire multi-phase 110km route, when completed, will link Dublin to Waterford.
The planned N9 will stretch from its junction with the N7 at Kilcullen in Co Kildare down to the Waterford bypass.
At the southern end, it will connect into the N25 to Waterford, Rosslare and Cork while at the northern end, the N9 will connect into the N7 which in turn connects to Dublin, Limerick, Portlaoise and Belfast.
Phase one, the 19km N9 Carlow bypass, has been in construction since last year. It is due to be completed next year.
The contract for phase three — the Kilcullen to Carlow section — is due to be awarded later this year and construction will begin in 2008.
The final leg of the project, linking the end of the route with the Carlow bypass, will commence construction in 2008 with a 2010 completion date.
Mr Cullen yesterday said: “This Government is committed to the creation of a road network that will promote regional and national competitiveness. It is also crucial to continue Ireland’s future economic competitiveness.’’
He added: “As 98.3% of our internal merchandise trade is carried on our road network, it is vital that we develop and build a world-class roads system, especially between the major urban centres.”
When the entire M/N9 road project is completed, towns such as Thomastown, Gowran, Paulstown, Stoneyford, Knocktopher, Ballyhale and Mullinavat will benefit from traffic decreases.
On the issue of road safety, Mr Cullen claimed: “The high quality dual carriageways and motorways we are building have been proven to be seven times safer than the roads they are replacing.
“This of course does not reduce the responsibility on all of us as individuals to drive carefully, to respect other road users, including cyclists and pedestrians, to observe speed limits and never to drink and drive.”
Peter Malone, chairman of the National Roads Authority, said the NRA was on target to deliver the major inter-urban routes by 2010.