Sekiguchi moved up to the All-Japan Formula Three Championship in 2007, driving for the Now Motor Sports team owned by Naohiro Fujita.

In late 2008, Sekiguchi competed in the first round of the 2008–09 GP2 Asia Series season for the David Price Racing team.

Sekiguchi made his Super GT debut in 2007, partnering 2002 GT500 champion Akira Iida at Racing Project Bandoh.

In just his fifth race at Sportsland Sugo, Sekiguchi drove from behind and passed Shigekazu Wakisaka with just a few laps remaining to take the win.

[4] In doing so he became the youngest GT300 class winner at the time, at 19 years, 7 months of age (a record which would be broken in 2008 by Keisuke Kunimoto).

[5] Sekiguchi would later serve a one-race ban during the September round at Fuji for reaching ten penalty points under the Driving Moral Hazard Prevention System.

Sekiguchi finished every race in the points for the second year in a row, and was fourth in the standings alongside Kunimoto.

Sekiguchi and Tsuboi went into the final round at Fuji trailing championship leader Naoki Yamamoto by 16 points.

They won the race from fourth on the grid, and after Yamamoto was involved in an accident with Honda GT300 driver Ren Sato, Sekiguchi, Tsuboi, and TOM'S would win the GT500 championship after overcoming the largest point deficit in the final round of the season.

At Sugo, Sekiguchi won from pole position after building up a 14-second lead when the safety car was deployed following a spin by teammate João Paulo de Oliveira.

[10] In the 2019 round at Autopolis, he won from 16th on the grid, setting the record for the lowest starting position by a race winner in series history.

[11] And in 2022, Sekiguchi fought off team-mate Ryo Hirakawa to win the second race of a double-header at Motegi, for his first victory in over three years, and his last in the series.