However, NUP leaders have rejected the results, alleging electoral irregularities and insisting that their candidate won the contest.
The by-election was held to fill the parliamentary seat left vacant following the death of former Kalangala District Woman MP Helen Nakimuli.
According to official results announced by Kalangala District Returning Officer Ronald Agaba in the early hours of Thursday morning, Nabayigga secured 12,642 votes against Nampala’s 7,474 votes.
Independent candidate Sharifah Kaala garnered 244 votes, Hellen Flavia Nagawa received 217 votes, while Nassuuna Agnes polled 34 votes.
The tallying exercise began shortly after 8pm on Wednesday as Electoral Commission officials compiled results from polling stations across the island district.
NRM supporters were the most visible political group at the district tally centre alongside election officials and accredited observers.
Shortly after the declaration, celebrations broke out among NRM supporters as Nabayigga thanked voters for what she described as renewed trust in her leadership.
“This victory belongs to the people of Kalangala. I am ready to continue serving them and to pick up from where I left off during my previous term,” Nabayigga said.
Senior NRM leaders, including the party’s National Mobilisation Chairperson Rose Sseninde, welcomed the outcome, describing it as a reflection of public confidence in the ruling party and pledging continued support for development programmes in the district.
“The people of Kalangala have chosen continuity and development. We expect government programmes to move even faster for the benefit of residents,” Sseninde said.
However, shortly after the declaration, NUP leaders led by the party’s Head of Mobilisation Habibu Buwembo and Deputy Secretary General Aisha Kabanda rejected the outcome and vowed to challenge the results.
“We do not accept these results. We believe the people of Kalangala voted for change, and we shall soon announce our next course of action,” Buwembo said.
The opposition leaders maintained that their candidate, Iren Nampala, had won the election and accused the Electoral Commission of presiding over a flawed process, though they did not immediately provide evidence to support the claims.
The disputed outcome sets the stage for a possible legal and political challenge as attention turns to the next steps NUP says it will announce in the coming days.