[1][2] Born in Chiba, Japan, Harada won the Japanese 125cc Junior championship in 1988, and was runner-up to Tadayuki Okada in the All-Japan 250cc series in both 1990 and 1991, before taking the crown in 1992.

[1][2] In 1998 Harada battled his Aprilia teammate Capirossi for the championship, leading for most of the season, until the two riders were involved in a controversial incident at the final race of the year in Argentina.

In 2001 he made another attempt to obtain a second 250cc world championship, taking 8 poles and three victories: the title, however, went to fellow Japanese Daijiro Kato.

[1] For 2002 he entered the MotoGP class aboard a Honda two-stroke, but this proved to be his final year of professional racing, as he retired after a difficult season that saw him finish 17th overall.

[1] Points system from 1988 to 1992: Points system from 1993: (key) (Races in bold indicate pole position; races in italics indicate fastest lap) 1949  B. Ruffo 1950  D. Ambrosini 1951  B. Ruffo 1952  E. Lorenzetti 1953  W. Haas 1954  W. Haas 1955  H. Müller 1956  C. Ubbiali 1957  C. Sandford 1958  T. Provini 1959  C. Ubbiali 1960  C. Ubbiali 1961  M. Hailwood 1962  J. Redman 1963  J. Redman 1964  P. Read 1965  P. Read 1966  M. Hailwood 1967  M. Hailwood 1968  P. Read 1969  K. Carruthers 1970  R. Gould 1971  P. Read 1972  J. Saarinen 1973  D. Braun 1974  W. Villa 1975  W. Villa 1976  W. Villa 1977  M. Lega 1978  K. Ballington 1979  K. Ballington 1980  A. Mang 1981  A. Mang 1982  J. Tournadre 1983  C. Lavado 1984  C. Sarron 1985  F. Spencer 1986  C. Lavado 1987  A. Mang 1988  S. Pons 1989  S. Pons 1990  J. Kocinski 1991  L. Cadalora 1992  L. Cadalora 1993  T. Harada 1994  M. Biaggi 1995  M. Biaggi 1996  M. Biaggi 1997  M. Biaggi 1998  L. Capirossi 1999  V. Rossi 2000  O. Jacque 2001  D. Kato 2002  M. Melandri 2003  M. Poggiali 2004  D. Pedrosa 2005  D. Pedrosa 2006  J. Lorenzo 2007  J. Lorenzo 2008  M. Simoncelli 2009  H. Aoyama 2010  T. Elías 2011  S. Bradl 2012  M. Márquez 2013  P. Espargaró 2014  T. Rabat 2015  J. Zarco 2016  J. Zarco 2017  F. Morbidelli 2018  F. Bagnaia 2019  Á. Márquez 2020  E. Bastianini 2021  R. Gardner 2022  A. Fernández 2023  P. Acosta 2024  A. Ogura