This study did a content analysis on readers' comments to online-newspaper reports of the 2015 presidential election in Nigeria. Using two online newspapers as a case study, readers' comments on randomly selected 10 political news stories in the 30 days prior to the election were used as samples. Readers' comments were rated based on their analytical and persuasive content. An opinion survey of 200 voters following the election was also conducted to justify the influence of the comments on voting behaviour of readers. Using gate-keeping and public-agenda in readers' comments as theoretical underpinning, this study found that the direction of more than three-quarter of online readers' comments influenced the voting behaviour for more than 90% of online-newspaper audience. It concluded that the platform could be an avenue not only to boost political campaigns but also to measure public opinion on political issues.