Takagi made his debut in the All-Japan GT Championship (JGTC) in 1998, driving for INGING in the GT500 class.

For the 1999 season, he switched to the GT300 class, finishing third in the championship that year.

He won his maiden title in 2002 with Autobacs Racing Team Aguri (ARTA), driving an apr Racing [ja]-prepared Toyota MR-S alongside Morio Nitta.

[3] In the following years, with the series renamed as Super GT in 2005, Takagi won numerous races and finished runner-up in the standings in 2004, 2008, 2010 and 2018.

In 2019, he won his second GT300 championship seventeen years after his first, driving the Honda NSX GT3 Evo of ARTA, with Takagi and his co-driver Nirei Fukuzumi finishing over ten points clear of the second place finishers.