The Government gave the green light for a long-term lease at the new building last week, it is understood, meaning the landmark building is now mostly occupied.
The giant 100,000 sq ft office will now undergo a major fitout to be ready for work to start in 22 months.
Up to 1,500 jobs are to be created in the city, from construction posts to designers and surveyors, as a result of the new city base which will oversee the building of the £50 billion rail scheme.
It represents one of the largest employment boosts for the city in recent years and also the largest-ever public sector relocation to Birmingham.
The project is likely to create thousands of more jobs in the supply chain, with consultancies and engineering firms expected to want to follow HS2 to the city.
Two Snowhill is also home to law firm Wragge Lawrence Graham & Co which occupies 185,000 sq ft.
In a separate announcement today, a new urban regeneration company is to be set up in Birmingham to lead developments around the site of the planned HS2 terminal in Curzon Street.
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