The Metaphysical movement, which is said to have begun at the start of the seventeenth century (1600s), preceded and overlapped John Milton's writing career as he was born in 1608 and some of his earliest notable works were written while in Cambridge around 1625-1626. Lists of Metaphysical poets include John Donne (1572 – 1631), the most notable of all metaphysical poets, George Herbert (1593 – 1633) and Andrew Marvell (1621 – 1678), who was younger than and secretary to John Milton, but exclude John Milton.
According to the Academy of American Poets, Metaphysical poets established a poetic mode that sought to unify thought and feeling in a meditational style and to employ reason in delving into philosophical and spiritual subjects they addressed in poetry. As the leader of the metaphysical poets, Donne centered his poetry on his personal spirituality as it interacted with realism in describing intimacy and with his analysis of what is now called human psychology. Though Milton isn't labeled as a Metaphysical poet, his stylistics share commonality with metaphysicalists on at least two points.
Firstly, Milton adapted his religious beliefs to suit his own understandings and held a spiritual view that reflected monism as he had adopted an animist materialist point of view. This spiritual belief held that everything from angels to souls to bodies to stones is composed of one single substance. Milton therewith solves the problem of mechanistic determinism attributed to Hobbes and the duality of mind and body described by Plato and Descartes.
Secondly, animist materialism, an approach to philosophical and spiritual questions from a heterodoxly reasoned point of view, is a key component of Milton's greatest work, Paradise Lost, while the legions of Satan both eat and engage in acts of intimacy. These features of Milton's work indicate an influence from the Metaphysical school, although critics don't acknowledge Milton as one of the metaphysicalists.
One reason that Milton is excluded is that while Milton shared at least these two points with them, he was also intently focused on the practicalities of political and social reform commentary as is confirmed by the pamphlets he wrote on many controversial topics such as advocacy of divorce, opposition to episcopacy (church governance by hierarchy) and opposition to reestablishing the monarchy.