Aged between 28 and 69, the group included democratically elected lawmakers and district councillors, as well as unionists, academics and others ranging from modest reformists to radical localists.
At their trial, judges said their plan to scupper the budget would have caused a “constitutional crisis”.
In 2024, the court convicted 45 people and acquitted two.
During the appeal hearing last year, defence lawyer Erik Shum said that lawmakers should be allowed to veto the budget as a form of “check and balance”, as stated in Hong Kong’s mini-constitution.
“In order to check the unpopular exercise of powers by the executive, one of the important measures is to tie the purse,” he told the court.
Shum said lawmakers should not be answerable to the courts over how they vote because of the separation of powers.
The 45 convicted campaigners were given sentences ranging from four years and two months to 10 years, depending on their role and whether they received reduced penalties.
Some of the appellants have already spent nearly five years behind bars.
As of last month, 18 other defendants who did not contest their convictions have been released after completing their sentences.
Prosecutors had challenged the acquittal of one of the two people found not guilty, lawyer Lawrence Lau.
On Monday, the court upheld the acquittal.