The first Eurostar train departing London from St Pancras International Station leaves at 05:25, arriving at Paris Gare du Nord at 08:50. Note that there is a one hour time difference between London and Paris.
Last train from London to Paris leaves St Pancras at 20:05, arriving at 23:26.
On weekends, Saturday and Sunday, the last train leaves London at 20:35 (8:35pm).
If you’re traveling to another city outside of Paris, but within the Ile-de-France region, you can buy train tickets, known as Billet Ile-de-France, from a different style ticket vending machine, a Billetterie Ile-de-France.