One primary theme of Warlight is the fragile nature of memory. Nathaniel spends much of his time reconstructing his childhood and youth, but he must acknowledge that his recollections are unreliable; he describes the pieces he is gathering as “unconfirmed fragments.” As Nathaniel tries to move past the childhood trauma of war and abandonment after their parents left him and his sister, Rachel, the author probes the theme of the constructed nature of family through the children’s relationship with their unusual caretakers, two men “who may have been criminals.”

Although the protagonist’s coming-of-age plays a central role, Michael Ondaatje’s novel is more than one man’s autobiographical reminiscence: at its core is a real mystery of what their parents’ jobs were, how their mother died, and perhaps if she did actually die.

Themes of patriotism and honesty contrasted with wartime expediency and the situational character of integrity also guide Ondaatje’s work. As Nathaniel is looking back from the 1950s at the earlier war years, the author signposts the ethical dilemmas of the upcoming Cold War, asking the reader to consider the full cost of replacing violent warfare with espionage and secrecy, including their impact on the agents’ families.

Michael Ondaatje's narratives usually contain the theme of childhood memory; other examples include the fictional perspective present in The Cat's Table and Michael Ondaatje's own childhood memories in Running in the Family.

Nathan's childhood perspective in Warlight transitions into a coming-of-age theme, in which he looks back on how his childhood was shaped by parental abandonment. Nathan reflects on how the absence of his parents made him stoic and independent to the point of isolation. This coming-of-age theme and lack of parental guidance is associated with his illegal work with the Moth and the Darter as he assists them in their greyhound smuggling operation.

Closely tied to Nathan's story of development are the themes of love, intimacy, and emotional dysfunction. Related to his tendency to isolate himself from the world, Nathan comes to understand how his youth influenced his issues with intimacy in adulthood.

Nathan comes to understand that the Moth had been his guardian, always watching over him. Nathan recognizes the love that both Agnes and Olive provided him: as a lover and as a friend, respectively. The most salient and emotional part of the novel for me is how Nathan spends years obsessively searching for signs of his parents in documents while working in the Foreign Office.