The event is scheduled to take place May 17 in Eidsvoll, Norway, where the country's constitution was signed, TheLocal.se reported.
On Monday, King Carl XVI Gustav and Queen Silvia of Sweden announced they would not be attending the celebration because they do not normally attend foreign countries' national days. However, that move stirred controversy because the signing of the Norwegian constitution also marks 200 years of peace between the Scandinavian countries.
The Swedish royal family also has ties to the signing as the Norwegian constitution was adopted by King Carl XIV Johan of Sweden when he became king of Norway in 1815, a year after the constitution came into force.
The Swedish Royal Court said in a statement Thursday the king and queen ultimately decided to attend the May 17 event.
"The king has decided that he, together with the queen, will be present at the special event in Eidsvoll on the occasion of the 200th anniversary of the Norwegian constitution," the statement said.
Olemic Thomessen, president of the Storting, the Norwegian Parliament, said: "This means the heads of state in all three Scandinavian countries, the main players in the dramatic events of 1814, will be represented."
Queen Margrethe of Denmark had already accepted her invitation.