[1] Horiuchi played for the Yomiuri Giants his whole career, from 1966 to 1983; he was an integral part of the team's ten Japan Series championships during that period (including nine in a row).

1972 was Horiuchi's finest season, as he went 26–9 with a 2.91 ERA and 26 complete games, again winning the Eiji Sawamura Award despite the fact that he led the league in hits and home runs allowed.

[citation needed] Horiuchi finished his career with 203 wins, earning him a spot in Meikyukai.

Receiving 101,840 preference votes nationwide, he ranked 13th on the LDP list[3] – the party received only twelve proportional seats – and was thus the top replacement candidate for a possible kuriage-tōsen, i.e. the first candidate to be elected without an additional vote if an LDP proportional seat in the 2010 class of Councillors fell vacant.

As a result, he became a member of the House of Councillors in the proportional representation segment of the class of 2010 in August 2013 as the replacement for Hirohiko Nakamura, who died on July 31, 2013.