Howell was acquainted with such eminent writers and thinkers as Edward, lord Herbert of Cherbury (q.v.) and Ben Jonson. On Jonson's death in 1637 he wrote a tribute in the form of an elegy. His political allegory, Dodona's Grove, was translated into French and Latin, and England's Teares, an appeal for peace in 1644, was rendered into Latin and Dutch. In his political pamphlets he espoused the king's cause while he lived, but when Cromwell was made Protector, Howell praised him for dissolving the Long Parliament. Moving with the times, Howell laid himself open to the charge of inconsistency.

A gifted linguist, Howell compiled an English-French-Italian-Spanish dictionary, as well as a collection of proverbs derived from these languages and from Welsh. Fully conversant with Welsh, he never loses an opportunity to quote from his native tongue and to refer to what he considered the racial and linguistic affinities of his people.

As a writer he is now chiefly remembered for his Familiar Epistles. Into them Howell pours all his knowledge of men and affairs and his insatiable curiosity in many fields. Their liveliness has combined with their natural style to win for them a lasting popularity.