Judges dismissed all claims made by Labour Party candidate Peter Obi, including fraud, charges the electoral authority broke the law and allegations Tinubu was not eligible to run.
“This petition is hereby declared unmeritorious,” one of the judges said in the Abuja courtroom after more than six hours reading out their detailed judgment.
The court was also set to read its judgment on the second major opposition claim.
Filed by Peoples Democratic Party (PDP) candidate Atiku Abubakar, it lays out similar complaints against the February 25 election results.
The challenges came after one of the country’s most tightly fought elections, where former Lagos governor Tinubu won 37 percent of the vote, beating Abubakar and Obi to secure the presidency of Africa’s most populous nation.
The decision will most likely now to head to appeal in the Supreme Court, which has never ruled to overturn a Nigerian presidential election since the country returned to democracy from military rule in 1999.
Legal teams in white wigs and black robes packed into the courtroom early Wednesday to hear judges read through each detail of the lengthy judgment.
Judges had also earlier dismissed a smaller opposition claim to annul the election.
Security was heightened around the court in the Nigerian capital, with police and defence forces cordoning off access to the building with roadblocks.
Tinubu’s government had dismissed all claims of wrongdoing and appeared confident before Wednesday’s decision.
Tinubu took office at the end of May and has quickly introduced a set of reforms the government says will help put Africa’s largest economy back on track.
He is in India for the G20 summit, where he hopes to drum up foreign investment.
Nullify or verify
The 2023 election was one of the most contested in the country’s modern history, thanks in part to the emergence of a major third-party candidate, Obi, to challenge the dominance of Tinubu’s All Progressives Congress (APC) and the PDP.
Obi looked to appeal to younger voters who said they were hoping for an alternative to the old-guard candidates.
To improve transparency, the Independent National Electoral Commission (INEC) introduced biometric technology and IReV, a central database for uploading results in real time.
INEC acknowledged “glitches” but dismissed claims the vote was not free and fair. But critics had said the technical problems and delays had allowed opportunities for vote manipulation.
In two major lawsuits, the PDP and Labour called for the results to be nullified and for their candidates to be declared the winner or for the court to order a rerun.
The PDP’s Abubakar called the vote a “rape of democracy.”
The party says it presented proof that INEC broke electoral law in its transmission of results, and that Tinubu failed to meet constitutional requirements.
Labour’s lawsuit followed similar allegations, referencing INEC breaking electoral law, vote rigging and also claims Tinubu was not qualified to run.
The court ruling comes as Nigerians struggle with a rising cost of living after the government ended a fuel subsidy programme that kept petrol prices low and also freed up the naira currency.
Government officials say the policies are needed to revive the economy, calling for patience and supplying state governments with funds to help offset the impact.
Tinubu’s government is also tackling huge security challenges, from jihadists still fighting a long war in the northeast to inter-communal clashes and kidnap gangs operating in other regions.