Theoretical History and Historiography are essentially, the same fields. Both attempt to understand History as a causal and meaningful process and not simply to interpret History as a series of explainable events.
The field of Theoretical History has its roots in the Modern era-(though perhaps one could date the origins of Theoretical History or Historiography to an earlier time). Philosophers, such as George Hegel and Karl Marx were interested in understanding the cyclical-(or Dialectical) nature of Historical time and reality.
For both Hegel and Marx, History, had a deeper, more esoteric meaning that was (apparently) evident in the process of reconciled opposites. An event would appear or unfold, though such an event had an inherent opposite-(almost like an alter ego), that was inseparable. This opposite or "antithesis", (despite its inseparability), would also exist as an independent event. However, as time progressed, both of these opposing events would join together, thereby creating, yet, another independent event and thus, the historical process continues.
Over the last half century, the post-modern theory has both transitioned from and greatly transformed contemporary western historiography and the philosophy of history. The post-modern approach is unconcerned with cyclical, exotic processes, but rather, more concerned with the radical "deconstruction" of knowledge and absolute truths-(Even Hegelian and Marxian Dialectics, are not exempt from the post-modernist's deconstructionist agenda). Post-Modern has and continues to approach knowledge and truth from a relativistic perspective.
If, for example, Culture A believes something to be true and Culture B believes something to be true, then under the logic of post-modernism, both the belief systems of Cultures A and B are equally and unquestionably true. Ordinarily and from a common sense perspective, such a narrative-(including, a historical narrative) would appear to be absurd and contradictory. Yet, for nearly 50 years, the radical philosophy of post-modernism-(including contemporary historiography), has become, "the opiate"-(to borrow an old famous phrase) of the academic intelligentsia and currently shows no signs of decline or disappearance.
There are other types of theoretical history and historiography, however, the ones mentioned, are some of the more well known and well regarded in the academy-(and related institutions).