As Prince of Sukhodaya, he was a member of the Privy Council to King Rama VI, and was heir presumptive after the death of Prince Asdang.  The prince became King Rama VII on 25 February 1926.

His Majesty came to the throne during a period of change around the world.  After the fall of the Austria-Hungary empire and the end of Imperial Russia, people around the world were looking for change, mostly though to an end of monarchic rule, and Siam was no exception.  The King carried on studying the change to a Constitutional Monarchy started by his brother, King Rama VI, but still he believed that the Siamese people were not ready was such a change, and in an abrupt manner, but rather a gradual one.  But, with change sweeping around the world, a group of Siamese educated individuals, mostly from France and under the Royal Patronage, demanded this change.  The King finally gave in and granted constitution to the people of Siam on 10 December 1932.  Being a product of absolute ruling, he found that he was not the right person to rule the land, so he abdicated in 1935.  His Majesty spent his last years quietly with his wife, Her Majesty Queen Rambi Barni, in England.  They did not have any children.

His Majesty King Rama VII died childless in 1941, at the age of 48.

Although change had finally come to Siam in 1932, the Siamese people were lost without their king.  They have lived for centuries under an absolute kingship, and with the new leader in the form of a Prime Minister, it was just difficult to adjust.  They nevertheless still looked to the king for comfort, and as the father of the kingdom, the same as always.