Senator Umar Al-Makura (APC-Nasarawa South) has lost his re-election bid to Mohammed Onawo of Peoples Democratic Party (PDP).
Declaring the result on Monday in Lafia, Ahmed Ashiku, the state Returning Officer, said Mr Onawo got 93,064 votes to defeat Mr Al-Makura, a former governor, who polled 76,813 votes.
Mr Ashiku declared that Mr Onawo, having satisfied the law requirement and scored the highest votes, was returned elected.
Reacting to the outcome of the result, Francis Orugu, the state chairman of PDP, described it as a victory for democracy.
The APC is yet to comment on the outcome of the poll.
Mr Al-Makura was elected Governor of Nasarawa state in 2011, running on the Congress for Progressive Change (CPC) ticket.