Faiz Siddiqui claims he received "inadequate" teaching on his specialist subject course on Indian imperial history, which led to him getting a 2:1 back in 2000.
The 39-year-old, who studied modern history at Brasenose College, said the second-class degree meant a loss of earnings in his future career as a lawyer.
"Whilst a 2:1 degree from Oxford might rightly seem like a tremendous achievement to most, it fell significantly short of Mr Siddiqui's expectations and was, to him, a huge disappointment," his lawyer Roger Mallalieu told the High Court at an ongoing hearing this week.
expectations," he said.
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Siddiqui claims he was the "victim of poor teaching" due to staff being absent on sabbatical leave. He also alleges that medical information about his clinical depression and insomnia was not submitted to the examiners by his personal tutor.
He went on to work at some leading law and accountancy firms in the UK but has been unemployed for a few years. Oxford University denies negligence and believes the case was brought "massively" outside the legal time limit.
"The University of Oxford is robustly defending the claim brought by Mr Siddiqui. It is not appropriate for the institution to make any further comment while there is ongoing litigation," a university spokesperson said.
"Whatever teaching he received was sufficient to enable him to do well in his mock exams. Because he did not on the day was nothing to do with teaching at all," Milford said.
Justice Foskett will rule on liability in the case with any damages to be decided later if Siddiqui's claim succeeds at the end of the High Court hearing, expected to conclude by next week.
The case is seen as a crucial one for educational institutions as it could lead to similar claims by students unsatisfied with the teaching they receive.