Woolley is always quick to point out the physical impossibilities of Sir Humphrey's or Hacker's mixed metaphors, with almost excessive pedantry. He can occasionally appear rather childlike, by making animal noises and gestures or by acting out how such an analogy cannot work. Even so, on many occasions Sir Humphrey describes Woolley as a "rising star" and "high flier" of the Civil Service, though it is not entirely clear how to interpret Sir Humphrey's remarks — that is, whether with sincere deference to Bernard's capabilities or with indignance to such a term being applied to a subordinate.
Woolley plays an important role in many episodes in helping Hacker. For example, in "Doing the Honours", it is his idea that leads to Hacker proposing a scheme that links national honours to departmental economies (and he is quick to remind the Minister that he didn't suggest it, if asked). He seems to have studied past civil service actions in depth, occasionally recommending historically proven responses (such as the "Rhodesia Solution" for a potential arms scandal in "The Whisky Priest").
His background is not something revealed to any great extent, though we do find out (passim in the very last episode) that Woolley, like Sir Humphrey, is an Oxford graduate. (The novelisation, in an apparent mistake, refers to Bernard at one point as a graduate of Cambridge, but later follows the series in confirming that he attended Oxford. There is, however, no problem in suggesting that he attended both.) In addition, several areas of specialist knowledge surface from time to time: one example arises in "The Greasy Pole" where, while discussing the possible political dangers of building a chemical facility in the north of England (to manufacture the fictional compound "metadioxin"), Woolley is quick to remind Sir Humphrey that Greek, unlike Latin, has no ablative case.
Woolley is often the source of much exposition, serving in some ways as a proxy for the audience. His common sense views lead him to ask apparently sensible questions of Sir Humphrey, which are generally used to demonstrate his superior's rather more counter-intuitive view of the situation. Much of the satire comes from the fact that Sir Humphrey's views are not just shared by other experienced civil servants, but are taken completely for granted. Bernard's naïve questioning is the perfect way of bringing this out for the audience. In one such conversation, in "The Devil You Know", Bernard will simply not let the matter rest and eventually homes in on the heart of the issue. He begins the sentence, "But surely, in a democracy..." and is immediately dismissed by an exasperated Sir Humphrey. In "A Victory for Democracy", Bernard is genuinely outraged when he learns that the Foreign Office is conducting its own policy with little regard for the Prime Minister's wishes.
On the other hand, we frequently see Bernard forced to hide something, at which point he tries to mimic Sir Humphrey's distinctive style of confusing never-ending sentences in order to play for time with the Minister. An example of him attempting to "walk the tightrope" in this way occurs in "The Skeleton in the Cupboard", when he has to conceal a betrayed confidence from Hacker. Although he becomes slightly more adept at this over time, he is clearly much less proficient. At other times, he is the one explaining to the Minister how the civil service machinery works. When asked by Hacker if "...all this is to prevent Cabinet from enacting its policies?", Woolley casually and earnestly replies, "Well, someone's got to."
Woolley, like the Minister and Sir Humphrey, progresses through the series, especially in his understanding of political mastery. In the last scene of "The Tangled Web", the final episode of Yes, Prime Minister, Woolley of his own accord both saves Sir Humphrey from public embarrassment and gives Hacker a lasting weapon to use against him, by acquiring a tape of Sir Humphrey describing the British public in many unpleasant ways, spoken off the record after a radio interview. This act of service to the Prime Minister can be seen as the final result of many series' wrestling between the two competing loyalties. Throughout both series, Bernard is the only civil servant portrayed with any sense of conscience, seeking constantly to justify his actions to himself. In the final episode, therefore, he realises that his principal loyalty must be to the (Prime) Minister, and his intervention in the crisis is crucial in saving Hacker's political reputation and in ensuring that the Cabinet Secretary, like any other civil servant, remains a "humble functionary".
As with the other principal characters in the series, both actor and character have the same date of birth. This means that Bernard is in his mid- to late-forties during the series. Bernard is also married: in the Yes, Prime Minister episode "The Key", he declares that he does not give the key to his house to his mother-in-law. However, his wife never appeared in the series.