You can visit the official website of PBP for latest updates on registration at: https://www.paris-brest-paris.org/en/
In order to register for PBP, you need to qualify by completing a full SR series (200, 300, 400 & 600) in the year of PBP. For PBP 2027 edition, you must complete an SR series between 1st Nov 2026 and 30th June 2027.
If you wish to get a priority starting time and confirm your participation slot well in advance then you must pre-register for PBP. The pre-registration window will open in order of priority based on the longest distance brevet you completed between 1st Nov 2025 and 31st Oct 2026. So a person who completed 1000 Km or longer brevet will get to pre-register for PBP before someone who completed a 600 Km and so on. The schedule for pre-registration and registration is posted on the official PBP site.