I have been trying to figure out how to get from London to Calais without a car. My husband and I will be in London for four days without a car and will be picking up a car in Calais. I see a train runs to Lille, but does it stop in Calais?
I don't believe so. Looks like you have to change in Lille and take a train back to Calais. According to Rome2Rio there's also a bus and ferry option or a train and ferry option. Both of those would take you to Calais and not Lille.
Some Eurostar trains used to stop at Calais-Fréthun station (from where a taxi could get you wherever you need), but I am not sure if this is still the case with the reduced Covid schedule.
Otherwise, rather than going to Lille and backtracking, it is probably more fun to take a train to Dover and a ferry to Calais.
EDIT: see below, I was not aware that the ferries were no longer accepting foot passengers. So, Lille it is! Any way you could change you car reservation to Lille? It might be more convenient in the end.
When are you travelling?
At present, ferries on the Dover-Calais route are running a reduced schedule due to Covid and they are not accepting foot passengers. The same applies to the Eurostar, where trains are not stopping at Calais, so you would have to go to Lille then take a train back to Calais or hire the car from Lille. Lille is a beautiful place to spend a few hours.
Pre-Covid, not many trains stopped at Calais.
any reason why you couldn't get your car at Lille? The Lille Europe station has the rental offices right in the station and the garage is in the station too.
Calais has always been a real pain in the neck to get the car, by ferry or by one of the rare Eurostars before covid - it is a genuine non-starter now.
The schedules for the Dover to Calais ferries says they do not take foot passengers at this time.