Rightacres Property has awarded the company the contract to build the new UK Government Hub building at Cardiff's Central Square development.
At more than 270,000 sq ft, the 12-storey building will be one of the largest office buildings ever built in Wales and will be capable of accommodating more than 4,000 people.
Designed by architects Gensler and located on the site of the former Western Mail & Echo print works, the building is due for completion at the end of 2019.
HMRC will be one of the main occupiers, with the first wave of civil servants due to move into the new offices in 2020.
Paul McCarthy, Rightacres Chief Executive, said:
"Sir Robert McAlpine played a big part in helping us secure the Hub to Central Square. They have fantastic local team each of whom has an impressive portfolio and we look forward to working with them to deliver this project."
Secretary of State for Wales Alun Cairns said:
"This Government is committed to delivering the best quality public services in every corner of the UK. This new build is great news for Cardiff, and will deliver a range of benefits to people in the capital and beyond, from improved public space and transport, to employment opportunities during construction."