Built 1855 to the designs of John Robinson this 'wedding cake' building was originally the head office of the Bank of Mona, a subsidiary of the City of Glasgow Bank, which had arrived on the Island in 1849. In 1878 its parent bank collapsed and the Bank of Mona, though itself solvent, was forced to close.
Brown's guide of 1894 states:
In 1879, these premises were bought by the Insular Government, and altered to meet the requirements of the executive departments, and of the legislature. The sessions of the Council and the Keys, when sitting as separate branches of the legislature, are held in these buildings; but, when sitting together, as the Tynwald Court, they are still held in the Douglas Courthouse. This latter building, however, is not suitable for this purpose; and more convenient and better arranged buildings are now in course of erection upon a site adjoining the Government Building.
See A.N. Laughton (Chap XXVI) for one version of the embezzlement at the Bank by Chief Cashier Gray in 1875.
The buildings were renovated 2004 - though it was planned to return them to their original red colour which better matches the adjoining Tynwald chamber as seen in the 1896 photograph, public opinion wanted the white to be retained.
1896/7 photo from Mate's Guide
- the 'tram' is the Upper Douglas cable car
Tynwald A Centenary of the Tynwald Chamber Tynwald:Douglas nd 
J. Brown gives a detailed account of the movement of the Courts and Tynwald from Castletown to Douglas in Historical Chapter (pp88-101) 1881 Directory.