Sekiguchi entered motorsport in 2004 after winning a Toyota scholarship to compete in the Japanese Formula Toyota series. He contested Asian Formula Renault part-time before stepping up to the All-Japan Formula Three Championship in 2007 with Now Motor Sports. In 2008, he moved to Europe to race in the International Formula Master, finishing sixteenth overall with two fourth-place results at Imola and Monza. He briefly appeared in the GP2 Asia Series that winter for David Price Racing before being replaced after the opening round.
Returning to All-Japan Formula Three in 2009, Sekiguchi steadily improved his results over successive seasons. He joined ThreeBond Racing in 2010 and finished second in the championship with three victories. A switch to B-Max Engineering in 2011 brought the series title, secured with six race wins. He subsequently made appearances at the Macau Grand Prix in 2011 (finishing fourth), 2013, 2015, 2017, and 2018.
Sekiguchi made his Super GT debut in 2007 in the GT300 class, partnering former champion Akira Iida at Racing Project Bandoh. In just his fifth race at Sportsland Sugo, he passed Shigekazu Wakisaka in the closing laps to claim victory, becoming the youngest GT300 winner at the time at 19 years and 7 months of age. He raced with various GT300 teams through 2012, including a stint with NDDP Racing where he and Katsumasa Chiyo scored the Nissan GT-R's first GT300 race win at Sugo.
Sekiguchi stepped up to the GT500 class in 2013, joining MOLA alongside three-time champion Satoshi Motoyama. The following year he transferred to Lexus and reunited with Racing Project Bandoh, driving alongside three-time champion Juichi Wakisaka. In 2016, partnered by Yuji Kunimoto, he scored his first GT500 victory at Buriram International Circuit in Thailand from pole position, a significant result for the Bandoh team whose previous GT500 win had come six years earlier.
Moving to TOM'S Racing in 2018, Sekiguchi won the Fuji GT 500 Mile Race that year and the Suzuka round in 2019, both alongside co-driver Kazuki Nakajima. The 2021 season brought his greatest success: paired with Sho Tsuboi at TGR Team au TOM'S, he entered 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 eliminated in an incident with a GT300 car, Sekiguchi and Tsuboi claimed the GT500 title after overcoming the largest final-round deficit in series history.
He moved to TGR Team SARD in 2022, reuniting with Juichi Wakisaka, now serving as team director.
Sekiguchi spent eight seasons in the Super Formula Championship with Team Impul, debuting in 2016 alongside reigning GP2 champion Stoffel Vandoorne. He finished third in the championship in his debut year, taking wins at Twin Ring Motegi and Sportsland Sugo. At Sugo he built a 35-second lead before pitting and won by over 14 seconds without relinquishing the lead, despite a safety car period.
He held off Pierre Gasly by 0.243 seconds to win again at Sugo in 2017. A particularly dramatic result came in 2019 at Autopolis, where he won from 16th on the grid — setting the series record for the lowest starting position from which a race has been won. He accumulated seven victories, six pole positions, and 13 podiums across 65 Super Formula starts, finishing as high as third in the championship twice (2016 and 2021). He was released from the Toyota Super Formula roster following a pointless 2023 season.
Sekiguchi's career illustrates the trajectory of a Toyota-affiliated driver progressing through Japan's domestic ladder. His 2021 GT500 title — secured in the final round from a seemingly impossible points deficit — stands as one of the most dramatic championship conclusions in Super GT history.