A manuscript-by-manuscript listing of the holdings of the office can be found here.
Many of the documents now part of the general manuscript series simply derive from the paperwork necessary for running an office. These include cash books, receipts, Ulster's diaries, letter books, day books and records of fees due for the various functions carried out by Ulster. Of these the most interesting from a genealogical point of view are the letter books (GO361-78), copies of all letters sent out from the office between 1789 and 1853; and the Betham letters (GO 580-604), a collection of the letters received by Sir William Betham between c.1810 and 1830 and purchased by the Genealogical Office in 1943. The former are indexed volume by volume; the latter are of more potential value. The only index, however, comes in the original catalogue of the sale of the letters, dated 1936, a copy of which is to be found at the office, though not numbered among the manuscripts. The catalogue lists the letters alphabetically by addressor, and a supplementary surnames index provides a guide to the families dealt with. Another eight volumes of the series, unindexed, are to be found in NAI (M.744-51).
As well as documents produced in the day-to-day running of the office, a large number of manuscripts relate to the ceremonial functions performed by Ulster. These include official orders relating to changes of insignia, papers dealing with precedence and protocol, records of official functions at the Viceregal court, and the records of the Order of St Patrick. There is little of genealogical interest in these.
In the course of their heraldic and genealogical work Ulster and his officers accumulated a large series of manuscripts for use as reference works. These include manuscript armories, ordinaries of arms, treatises on heraldry and precedence, a series of English Visitations, and blazons of arms of English and Scottish peers. The bulk of the material is heraldic, but there is a good deal of incidental genealogical information, particularly in the seventeenth-century ordinaries of arms.