Tajima was born in 1950 in Suginami, Tokyo, and began his competitive driving career in 1968 in the All Japan Dirt Trial Championship, winning his first race in his debut season. His entrepreneurial instincts matched his driving talent: in 1983 he founded Monster Sport International, a motorsport preparation and tuning business that would become the institutional backbone for his racing campaigns. Three years later, in 1986, he formalized his long-standing association with Suzuki by establishing Suzuki Sport, the manufacturer's in-house motorsport division.
Tajima's first World Rally Championship appearance came at the 1981 Lombard RAC Rally, where he entered a Datsun. His rally ambitions grew through the 1980s and 1990s as Suzuki's partnership deepened. He competed in the Olympus Rally in 1987 and 1988, earning class wins both years, finishing 15th and 7th overall respectively. Through the early 1990s he raced in the Asia-Pacific Rally Championship, piloting a series of Suzuki machinery — a Suzuki Swift, then a Suzuki Baleno Wagon Kit Car from 1997, and a Suzuki Ignis S1600 from 2001. He accumulated four WRC class wins and two Asia-Pacific Rally Championship class wins, and scored four championship points in the 1988 WRC season. He finished fourth in the 2001 Asia-Pacific Rally Championship drivers' standings.
When the Junior World Rally Championship project launched in 2002, Tajima stepped back from driving to become team manager of Suzuki Sport, overseeing the factory's competitive infrastructure. In 2006, at the Geneva Motor Show, he announced Suzuki World Rally Team's plans to field a Suzuki SX4 in the WRC, a program that ultimately debuted in 2008 following calendar changes.
It is at Pikes Peak where Tajima built his legend. Suzuki and Tajima began challenging the Colorado hillclimb in 1989. In 1993, driving a twin-engined Cultus, he won the Unlimited Division and finished second overall. In 1995, he became the first Japanese driver to win Pikes Peak outright, doing so in a twin-engined Escudo. From 1996 onward he became synonymous with the V6 Suzuki Escudo, a car that defined an era at the mountain.
After finishing runner-up three times — in 1996, 1998, and 1999 — Tajima returned to the top step in 2008, overcoming a practice crash to take the overall victory in a rain-shortened event, this time in a newer Escudo variant. He followed that with back-to-back wins in 2009 and 2010 in the Suzuki SX4, clocking 10:15.368 and 10:11.490 respectively.
On July 21, 2007, he had already broken Rod Millen's thirteen-year course record in his Suzuki Sport XL7 with a time of 10:01.408. Then on June 26, 2011, Tajima shattered his own record and became the first driver to crack the ten-minute barrier at Pikes Peak, posting a time of 9:51.278 in the Suzuki SX4 Hill Climb Special developed by Monster Sport. That run represented his seventh and final outright Pikes Peak win.
In 2012, Tajima pivoted to the electric class at Pikes Peak, citing environmental concerns. His Monster Sport E-RUNNER Pikes Peak Special led qualifying but a power transfer failure ended his run on race day. In 2013, he won the Electric class with a time of 9:46.530, placing fifth overall. In 2014, he set a new electric-class record at 9:43.90.
His 2015 campaign saw him drive the Tajima Rimac E-Runner Concept_One, developed in collaboration with Croatian manufacturer Rimac Automobili. He finished second overall in 9:32.401, behind Rhys Millen's 9:07.222. In 2016 he returned with the same car but fell to fifth overall and third among electric vehicles, posting a 9:51.978.
Alongside Pikes Peak, Tajima dominated the Silverstone Race to the Sky hillclimb held in the Cardrona Valley in New Zealand, winning eight times out of eleven events, including three consecutive victories from 1998 to 2000 with the V6 Escudo.
Tajima's career spans nine All Japan Dirt Trial Championship titles, four WRC class wins, two Asia-Pacific Rally championship class wins, seven outright Pikes Peak victories, and eight Race to the Sky wins. He was inducted into the Pikes Peak Hill Climb Museum Hall of Fame in 2016. His Monster Sport enterprise and his role in building Suzuki Sport ensured that his influence on Japanese motorsport extended well beyond his personal driving record.