Smith brought the case against Tracy Williams after she posted a series of derogatory remarks about him on an online discussion board run by Yahoo. Williams has been ordered to pay more than $29,500 (17,000 pounds) after being found guilty of libel.
The accusations, which included claims that Smith was a racist and guilty of sexual offenses, were made as part of an online discussion about the Iraq war in 2003.
Smith had argued in favor of the conflict, which prompted Williams to label him a "lard brain" and later to falsely claim that he had sexually harassed a colleague.
Williams' remarks were made under a pseudonym, and in 2004, Smith obtained a court order forcing Yahoo to reveal the identity of the poster. He then brought his case to the High Court, claiming that Williams had continued to abuse him online.
Judge Alistair MacDuff, who heard the case, ordered Williams to pay Smith $17,365 (10,000 pounds) in damages and never again to repeat the remarks, which he described as "seriously defamatory." Williams, who did not file a defense, must also pay 7,200 pounds in court costs.
Legal experts have suggested that Smith's victory could encourage other people to file libel lawsuits.
A landmark case in 2000, Godfrey v. Demon, established that , and this case looks to have set a similarly important precedent.
Graeme Wearden of ZDNet UK reported from London.