No, you do not necessarily need to have a Tomorrowland Account in order to buy a ticket.
If you already have a Tomorrowland Account, you can find the link to buy a ticket at the home page of your account. Your personal details will be automatically pre-filled. You can buy one ticket per account.
If you don’t have a Tomorrowland Account, you can buy your ticket in the official Tomorrowland Around The World ticket shop. You will be able to enter the shop through a link on the website. Make sure you create a Tomorrowland Account before the event with the same email address you have bought your tickets with.
It is not possible to enter Tomorrowland Around The World without a Tomorrowland Account. Please find all information about creating a Tomorrowland Account here.