| Cover | Oct. 07, 2021 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Oct. 7, 2021 |
| Entity File Number | 001-38916 |
| Entity Registrant Name | Bicycle Therapeutics plc |
| Entity Central Index Key | 0001761612 |
| Entity Tax Identification Number | 00-0000000 |
| Entity Incorporation, State or Country Code | X0 |
| Entity Address, Address Line One | B900 |
| Entity Address, Address Line Two | Babraham Research Campus |
| Entity Address, City or Town | Cambridge |
| Entity Address, Country | GB |
| Entity Address, Postal Zip Code | CB22 3AT |
| City Area Code | +44 |
| Local Phone Number | 1223 261503 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | true |
| Elected Not To Use the Extended Transition Period | true |
| Common Stock [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Ordinary shares, nominal value £0.01 per share |
| Security Exchange Name | NASDAQ |
| American Depositary Shares [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | American Depositary Shares, each representing one ordinary share, nominal value £0.01 per share |
| Trading Symbol | BCYC |
| Security Exchange Name | NASDAQ |
