Located at the very centre of Edinburgh Castle and at the highest point of Castle Rock is the tiny Norman Chapel dedicated to St. Margaret (1045-93) wife of King Malcolm III (c.1031-93). The chapel was most likely completed between 1110-20 by her youngest son, King David I (c.1080 - 1153), but there it is some evidence that it was built on top of an earlier chapel in which Margaret herself may have worshipped. This chapel was the only building spared by Robert the Bruce when he took over the castle. On his deathbed, Robert the Bruce set aside money for the restoration of the chapel.

St. Margaret's Chapel measures only 5m by 3m (17 feet by 11 feet), with a simple nave separated by a distinctly Norman arch from a stone-vaulted semi-circular apse. The chapel survived the many attacks on the castle itself but was altered in the 17th Century to act as a gunpowder store. In 1845, the antiquarian Sir Daniel Wilson (1816-92) rediscovered the chapel and it was restored on the orders of Queen Victoria in 1853. Further restoration work was undertaken in 1886 by the French architect Hippolyte J. Blanc (1820-97). Stained glass windows portraying Saints Andrew, Columba, Margaret and Ninian, together with patriot William Wallace, were inserted in 1922. The chapel was re-dedicated in 1934 and a new doorway created on the north side five years later.

Today the simply-decorated chapel is still in use and members of the castle garrison have the right to be married in it.