In April 2007, he ran as an independent in the Saitama Prefectural Assembly election and won a seat for the first time.[4] After winning the election, he received additional nominations from the LDP and joined the party. In April 2011, he ran in the Saitama Prefectural Assembly election with the LDP's official approval and was re-elected without a vote.[5]
In 2012, he ran in the 2012 Japanese general election from Saitama 12th district with the LDP's official approval. Toshikazu Morita, a member of the Saitama prefectural assembly, also announced his intention to nominate the LDP for Saitama 12th district, but since Nonaka received the nomination, he ran as an independent.[6] Nonaka was elected in Saitama 12th district after defeating Morita and Hiranao Honda, the former Democratic Party of Japan's former parliamentary secretary for Economy, Trade and Industry.[7]
In the 2014 Japanese general election, he ran in Saitama 12th district as an official LDP candidate. Although Toshikazu Morita, who ran for the PFG, appointed a former member of the LDP as the top adviser to the camp to expand the support of the conservatives,[8] Nonaka won.[9]
In 2017, he was appointed Parliamentary Secretary to the Minister of Agriculture, Forestry and Fisheries in the Third Abe Cabinet Third Reshuffled Cabinet.[10][11] In the 2017 Japanese general election in the same year, he ran from Saitama 12th district as LDP and defeated Morita Toshikazu, who ran from the Kibō no Tō, by 492 votes.[12][13] He was reappointed as Parliamentary Secretary to the Minister of Agriculture, Forestry and Fisheries in the Fourth Abe Cabinet, which was established after the election.[14]
In the 2021 Japanese general election, veteran party members such as Shigeru Ishiba, Yuko Obuchi, and Toshimitsu Motegi prematurely celebrated his re-election,[15] but lost to Morita, who won the race by a narrow margin. The Northern Kanto proportional representation block, which had been duplicated, revived proportionally, and was selected for the fourth time.[16][17]
