Nukaga was born in Asō, Ibaraki, now part of Namegata, Ibaraki. He graduated from Waseda University's Faculty of Political Science and Economics.^[1] After working as a reporter for the Sankei Shimbun, he entered politics and was elected to the House of Representatives for the first time in 1983. He joined the Tanaka faction when elected, but along with most of the faction he later joined the Keiseikai founded by Noboru Takeshita, which was later renamed the Heisei Kenkyūkai.

He was named Minister of State and Director General of the Japan Defense Agency on 30 July 1998, under Prime Minister Keizō Obuchi,^[3] serving in that position until November 1998, when he resigned due to a scandal.^[4] He was named Minister of State in charge of economic and fiscal policy, as well as IT policy, on 5 December 2000, as part of Prime Minister Yoshirō Mori's second cabinet,^[5] but he resigned on 23 January 2001, following criticism regarding 15 million yen he had received from the mutual aid foundation KSD. He said that his secretary had received the money and that it had been returned, but apologized and said that he took "final responsibility as a supervisor". Chief Cabinet Secretary Yasuo Fukuda said that the government believed Nukaga's explanation.^[4]

Nukaga served as chairman of the LDP Policy Research Council from September 2003 to September 2004. He returned to the position of Minister of State and Director General of the Japan Defense Agency on 31 October 2005, under Prime Minister Junichiro Koizumi,^[6][7] and remained in that position until September 2006.

He was appointed Minister of Finance by Prime Minister Shinzō Abe in a cabinet reshuffle on 27 August 2007.^[2] Following Abe's resignation on 12 September, Nukaga initially said that he would run for the position of LDP president (and thus Prime Minister) on 13 September, but, on 14 September, after meeting with Yasuo Fukuda, Nukaga announced that he would back Fukuda for the leadership.^[8] Following Fukuda's victory in the leadership election, Nukuga remained as Finance Minister in Fukuda's Cabinet, sworn in on 26 September 2007.^[9] He was replaced in that post by Bunmei Ibuki on 1 August 2008.

Nukaga was reelected in the August 2009 House of Representatives election, which was otherwise disastrous for the LDP. Nukaga was chosen to replace the retiring Yuji Tsushima as head of the Heisei Kenkyūkai. After the LDP returned to government with the 2012 election he became subcommittee chairman of the LDP Tax System Research Commission. In April 2015 he also became chief of the LDP "Headquarters for accelerating reconstruction after the Great East Japan Earthquake".^[10][11]

On 8 February 2018, Nukaga announced his intent to resign from his position as head of Heisei Kenkyūkai. This followed a rebellion in which faction members in House of Councillors led by Hiromi Yoshida threatened to leave the faction unless there was change in leadership. In March he handed over the leadership to Wataru Takeshita, the half-brother of the faction's founder. After that, Nukaga became chief advisor of the faction.^[12][13]

In September 2019 Nukaga left the position of subcommittee chairman and became an advisor of the LDP Tax System Research Commission. He remained an authority in the field of economic policy within the LDP. In December 2021 he was chosen as chief of the new LDP "Headquarters for promoting fiscal consolidation."^[14][15]

In October 2023 Nukaga was elected Speaker of the House of Representatives, after Hiroyuki Hosoda resigned due to health reasons.

Nukaga is affiliated to the conservative lobby Nippon Kaigi^[16]