Pieter Jansz Post was a Dutch Golden Age architect, painter and printmaker.

Post was baptised in Haarlem, the son of a stained-glass painter and the older brother of painter Frans Post. He is credited with the creation of the Dutch baroque style of architecture, along with his longtime collaborator Jacob van Campen. Together they designed the Mauritshuis in the Hague. According to Houbraken he was a famous architect who introduced his brother Frans to Maurice of Nassau, Prince of Orange while he was working on plans for the Mauritshuis.

According to the RKD he became a member of the Haarlem Guild of St. Luke in 1623, and became painter and architect for Stadhouder Frederik Hendrik. He was the overseer from 1640 for the new additions to Paleis Noordeinde in The Hague. From 1645 he was the architect for Frederik Hendrik for Huis ten Bosch, where he worked together with Jacob van Campen. He died in The Hague, aged 61. His son Maurits became an architect, and his son Johan Post became a painter, and his daughter married the anatomist and collector Frederik Ruysch. His granddaughter Rachel Ruysch became a famous flower painter.