This paper is devoted to study some topics of monotone operator theory in the context of Hadamard spaces. For a fixed element p in an Hadamard space X, the notion of p-Fenchel conjugate is introduced and a generalization of Fenchel-Young inequality is proved. Moreover, p-Fitzpatrick transform of a monotone set-valued operator from an Hadamard space X to its linear dual space X ◊ and its main properties are investigated. Finally, a characterization result for maximality of monotone operator T ∶ X ⊸ X ◊ , based on certain classes of proper, convex, l.s.c. extended real-valued function h on X × X ◊ , is given.