Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Mar. 05, 2021	Jun. 30, 2020
Document Information [Line Items]
Document Type	10-K
Document Period End Date	Dec. 31, 2020
Entity Registrant Name	BICYCLE THERAPEUTICS PLC
Entity Well Known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Interactive Data Current	Yes
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		23,090,382
Entity Public Float			$ 189,962,881
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Central Index Key	0001761612
Amendment Flag	false
Entity Ex Transition Period	true
Ordinary Shares
Document Information [Line Items]
Title of 12(b) Security	Ordinary shares, nominal value £0.01 per share*
None	false
Security Exchange Name	NASDAQ
American Depositary Shares
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