| Document And Entity Information | Jun. 16, 2022 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jun. 16, 2022 |
| Entity Registrant Name | PepGen Inc. |
| Entity Central Index Key | 0001835597 |
| Entity Emerging Growth Company | true |
| Entity File Number | 001-41374 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 85-3819886 |
| Entity Address, Address Line One | 245 Main Street |
| Entity Address, City or Town | Cambridge |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02142 |
| City Area Code | 781 |
| Local Phone Number | 797-0979 |
| Entity Information, Former Legal or Registered Name | Not Applicable |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Ex Transition Period | true |
| Title of 12(b) Security | Common stock, par value $0.0001 per share |
| Trading Symbol | PEPG |
| Security Exchange Name | NASDAQ |
