A notification was issued by chief secretary Utpal Kumar Singh after governor Baby Rani Maurya gave her assent to the move.
The chief minister dedicated the summer capital status to Gairsain and to the thousands of men and women of Uttarakhand who fought for its statehood.
Expressing happiness at the formal declaration, Rawat said Gairsain would be developed as the ideal capital of a hill state.
Making Gairsain the summer capital of the state was part of the Bharatiya Janata Party’s vision document for the 2017 assembly election.
Rawat said an action plan was being prepared to create suitable basic infrastructure there in consultation with planners and experts.
Work on creating an e-Assembly at Gairsain is underway so that files need not be taken there and sessions are conducted in a paperless way, he said, adding that it would promote paperless work culture in the state.
A lake is being developed on the Ramganga, a tributary of the Ganga, to streamline water supply in Gairsain and adjoining areas, including Bhararisain where the assembly is located, Rawat said.
According to the chief minister, work is also in progress on strengthening connectivity in Gairsain.
Rawat added that roads connecting Gairsain and Bhararisain would be widened as required, and work on the Rishikesh-Karnaprayag railway project, which would take tracks very near Gairsain, was also going on rapidly.
BJP vice president Devendra Bhasin said the party had fulfilled a major promise made in its poll manifesto.