Yes, you can make that journey with a pass, all British railways are included.

If this is part of a larger group of railway journeys in Europe the Global pass is probably the best ticket for you. If this is the only journey you are making then it would be cheaper to buy ordinary tickets.

Harlech is a small town there are no direct trains, 1, 2 or 3 changes would be required.

You can search times on this site http://www.nationalrail.co.uk/

Thank you very much indeed for your kind reply, which is really assuring to us.

Yes, travelling from London to Harlech is a part of our bigger railway journeys.

We plan to travel from Harlech to Liverpool the next day using Eurail Global Pass and stay one night there. From Liverpool, we will travel to Manchester by probably buying ordinary tickets at the station because it is relatively a short distance. Then we will fly to Germany.

We plan to restart Eurail Global Pass when traveling from Koblenz, Germany to Amsterdam. After staying for a few nights there, we will then go to Brugge by Eurail Global Pass.

Finally, we plan to return from Brugge to London, using Eurail Global Pass and Eurostar.

As above, I am planning to buy 5-Day Eurail Global Pass. Does this plan look reasonable to you, if you don’t mind my asking. 

Again, thank you very much for your reply. We haven’t been to the U.K. and Europe for a long time and as this is my first time to use Eurail Pass, I am really thankful to your suggestion.

All the best, 

If you are travelling this summer you should make your Eurostar reservation ASAP. 

There is a limited number of pass holder seats on the Eurostar between London and mainland Europe. On popular departures and during high season those sell out weeks, and sometimes months in advance.

The best place to see the availability of passholder seats and make reservations on the Eurostar is 

https://www.b-europe.com/EN/Booking/Pass#TravelWish

If you don't get any result, press "later trains" and eventually you will find the next available connection. 

If you have a mobile pass you need to generate a Pass Cover Number in order to make the reservation at b-europe. You do that here in the PCN generator:

https://community.eurail.com/news-and-announcements-39/pass-cover-number-generator-is-live-5653

Thank you very much indeed again for your help! i really appreciate it.

I have bought the Global Pass and made reservation at Eurostar. Thank you again.

I am checking the timetable from London to Harlech, and I saw there were “Anytime” and “Off Peak” trains in National Rail Enquiries.

For example, there is a train leaving London Euston at 08:40 and arriving at Birmingham International at 09:45. Then I will need to change the train to go to Harlech. I will take a train leaving Birmingham International at 10:08 and will arrive at Harlech at 14:22. It is an “Anytime” train, not “Off Peak”. 

My questions are:

1. Can I use the Global Pass to ride an “Anytime” train?

2. Is it possible to book the 2 trains with my Global Pass in advance? If yes, could you please tell me how I should do it? If not, can I just go to the London station to make a seat reservation with my Pass?
3. Can this journey be counted as 1 day travel in the Global Pass although I will use two trains?

I would appreciate it if you let me know. Thank you so much.

Anytime and Off-Peak are designations for regular fares.

With a Eurail pass you do not have to concern yourself with these, your pass is valid for all trains.

Reservations in UK are not required but you can get them for free either at a station ticket office or through the gwr.com website as described here

A pass day is any number of trains used in one day.

This is valuable information for me as a UK rail traveler.  I appreciate all of your answers.  Thank you very much indeed.