| Cover | 9 Months Ended |
| Sep. 30, 2021 | |
| Cover [Abstract] | |
| Document Type | 6-K |
| Entity Registrant Name | COMPASS PATHWAYS PLC |
| Entity Address, Address Line One | 3rd Floor |
| Entity Address, Address Line Two | 1 Ashley Road |
| Entity Address, City or Town | Altrincham |
| Entity Address, Postal Zip Code | WA14 2DT |
| Entity Address, Country | GB |
| Entity Central Index Key | 0001816590 |
| Document Fiscal Year Focus | 2021 |
| Document Fiscal Period Focus | Q3 |
| Amendment Flag | false |
| Current Fiscal Year End Date | --12-31 |
| Document Period End Date | Sep. 30, 2021 |
