Muf, which is considered one of the most promising of a new generation of architects, was selected last week ahead of six practices in the invited competition run by St Albans District Council.
The other firms invited to compete were Caruso St John, Hudson Featherstone, Panter Hudspith, Bere Architects, Peter Barber and St Albans-based Briffa Phillips.
Muf's visitor centre will enclose a Roman mosaic floor preserved in situ in Verulamium Park, the site of the ancient Roman city of Verulamium.
The mosaic floor, which covers a Roman heating system called a hypocaust, was part of a luxurious two-storey town house containing 30 rooms, excavated in the 1930s by Sir Mortimer Wheeler.
The new structure will replace a 1930s building described as "very utilitarian" in the competition brief. The park's Verulamium Museum houses most of the ruins of the town, the third largest in Roman Britain. Muf's scheme includes new paths linking the visitor centre and the Verulamium Museum, which will administer it.
The brief called for a "small but unique building", including a garden that would open up views to the medieval abbey.
Mark Suggett, museum director at St Albans District Council, said the council saw the building as a millennium landmark: "The idea was that the first millennium structure – the hypocaust – should be enveloped in a new, third millennium structure that has a significant relationship with the second millennium structure – the great Norman abbey – that overlooks it." Suggett said Muf's scheme "is a box you can see into and out of. You can see the reflection of the hypocaust before you get into it. Once inside, you can see the reflection of the abbey outside." He said Muf had thought as carefully about the path to the new visitor centre as about the building itself. "The scheme has a nice spatial relationship with what goes on around it in the park." Liza Fior, a founding partner of Muf, said the practice was delighted with the appointment. "We are very pleased. It is a lovely project." She added: "Muf has never made a qualitative distinction between its public realm projects and building projects. We have robbed the journalists of one of their straplines: 'Muf has never done a building.' " Muf's appointment is subject to confirmation by the planning and heritage committee of St Albans District Council.