On this site an earlier chapel – Capel Pentre Morgan – was built in 1804.
Seion Chapel was built on the new Holyhead Road in 1840 to cater for the increasing number of Wesleyan Methodists in the town. 
In 1860 the new Castle Street was built alongside.
In 1905 the new larger gothic style building that still stands today was opened on the same site.
