The money, from Parks Canada, will go toward repairing the roof, windows and leaks at Province House in Charlottetown.
The national historic site is commemorating 150 years since the 1864 Charlottetown Conference, which eventually led to Confederation.
Ottawa says a call for tenders for the work will be issued this year so that renovations can begin once anniversary celebrations come to an end.
Province House is the only provincial legislature maintained by Parks Canada.
The government also invested $2 million in 2011 to help preserve the building's masonry work.
The cornerstone was laid at Province House in 1843.