Sir John Marsham, 1st Baronet (23 August 1602 – 25 May 1685) was an English antiquary known as a writer on chronology.

After attending Westminster School he matriculated at St John's College, Oxford, on 22 October 1619; he graduated B.A.

In 1629 he went through Holland and Gelderland to the siege of 's-Hertogenbosch in Brabant; and then by Flushing to Boulogne and Paris in the retinue of Sir Thomas Edmondes, ambassador extraordinary at the court of Louis XIII.

After the surrender of Oxford he returned to London (1646), and having compounded for his estate, he lived in retirement at his seat of Whorn Place, in the parish of Cuxton, Kent.

Most of it was afterwards inserted in his more elaborate Chronicus Canon Ægypticus, Ebraicus, Græcus, et disquisitiones, London, 1672, a beautifully printed book (other editions, 4to, Leipzig, 1676, and 4to, Franeker, 1699, but both inaccurate).

He wrote also the preface to the first volume of Roger Dodsworth and William Dugdale's Monasticon Anglicanum (1655), which is entitled Propylaion Johannis Marshami; it is a complex survey of English monasticism.