The national ties between Finland and Sweden that endured for many centuries were broken following the war of 1808 – 1809 as a result of which Finland became an autonomous Grand Duchy of the Russian Empire. During the war itself, the Russian Emperor Alexander 1st ordered the Estates of the Finnish realm to assemble at the Diet in Porvoo in March 1809.

The members of the Diet gathered together on 25.3.1809 to examine the credentials. The opening ceremonies of the Diet began on the 28th of the same month in Porvoo cathedral after which the assembly adjourned to the ‘state rooms’ of the Porvoo Gymnasium building. There the Emperor declared the Diet open with an address in French which Governor General Sprengtport translated into Swedish. The following day, in an inauguration ceremony held at the cathedral, the Governor General read out the Swedish translation of the Act of Assurance signed by the Emperor on 27.3.1809 and the Estates declared their allegiance to the Emperor. In his Act of Assurance Alexander 1st declared he would uphold and reinforce the country’s religion and constitution as well as the rights and responsibilities of the estates of the realm and the inhabitants. Swearing the oath was facilitated by Gustav IV Adolf's abdication from the Swedish throne on the same day. Continuity was, however, ensured because Alexander 1st affirmed the 1773 Instrument of Government and the 1789 Act of Union and Security of Finland's constitution.

In total 134 representatives took part in the Diet though not all were present throughout. The nobles were represented by 77 members, the clergy by 8, the burghers by 19 and the peasants by 30. The spokesman for the nobles was Field Marshall Count Robert Wilhelm De Geer while the clergy’s spokesman was the Bishop of Turku Jakob Tengström. Also from Turku was the merchant Kristian Trapp who served as the spokesman for the burghers while the Senior Juror Petter Klockars from Uusikaarlepyy served in this role for the peasants.

The actual work of the Diet began on 30.3.1809. The Emperor had presented four bills for the Estates to consider. These concerned the formation of the Finnish Governing Council, forerunner of the Senate, a Bank of Finland, the levying of a crown tax and the organization of armed forces for Finland. Two committees were set up to deal with these bills. In addition to these matters put forward by the Emperor, members’ petitions that had been provided by those who had chosen them were also dealt with.

The work of the Diet was completed in July 1809. The closing ceremony was also attended by the Emperor and it was held in Porvoo on 19.7.1809. The spokespersons for the Estates presented their thanks to the Emperor and Justice Chancellor Tandefeldt read out the findings of the Estates in response to the proposals At this ceremony Alexander 1st gave the famous speech in which he stated that Finland had joined the ranks of the elevated nations.