U.S. studies have found that stratified graduate education accounts for most of the relatively strong intergenerational socioeconomic association among postgraduate degree holders. The same association has been observed, but not explained, in countries with higher education systems that differ from that of the United States. We explore the mediation role of undergraduate- and graduate-level stratification in accounting for the intergenerational occupational association among postgraduate degree holders in the United Kingdom. We find that the unequal distribution of undergraduate-level education and path dependency between undergraduate- and graduate-level stratification help to give rise to an unequal occupational outcome by social origin among postgraduate degree holders. We explain this by the tight coupling of undergraduate and graduate education in the United Kingdom. Our analysis also illustrates the need to go beyond graduate education in understanding social origin inequality among postgraduate degree holders to examine the role of undergraduate education and how it is linked to graduate education.