Tandja Mamadou (born 1938) is a Niger politician and current President.

Mamadou ran for President in the elections of 1996. At that time he was most notable for being a former interior minister of Niger. He received third place, 15.65% of the vote. He won the 1999 elections, however, receiving first place, 32%, in the first round, and 60% in the second round, defeating former Prime Minister Mahamadou Issoufou. Mamadou is the first democratically elected President of Niger after the coup that put Ibrahim Baré Maïnassara in power in 1996. In April of 1999, Maïnassara was assassinated and a new military government took over. This junta promised a return to democracy within the year, and the elections were held in October and November. Mamadou and his National Movement for the Development Society won the elections, and Mamadou took office on December 22, 1999. He appointed Hama Amadou as his Prime Minister.

Niger was heavily in debt and was not receiving any foreign aid due to Maïnassara's coup. Mamadou focused on economic development, negotiating with the civil service unions and with foreign donors. Many did not approve of Mamadou's measures in reducing government spending. In 2001, students at the University of Niamey staged violent protests against the reduction of their government grants. In 2002, some soldiers started a rebellion claiming that they were underpaid. Loyalists defeated the rebels and restored peace, but Mamadou came under political fire for his decrees blocking communication about the rebellion.

Mamadou's position was up for re-election in November 2004. In the first round of those elections, he got first place with 40.7% of the vote, the rest being divided between five opponents. As in 1999, Mahamadou Issoufu got second place, and participated in a runoff with Mamadou in December. Mamadou was re-elected with 65.5% of the vote, with Issoufou receiving the remaining 34.5%.