| Document and Entity Information | Nov. 04, 2021 |
| Document and Entity Information [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Nov. 4, 2021 |
| Entity File Number | 001-39231 |
| Entity Registrant Name | PASSAGE BIO, INC. |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 82-2729751 |
| Entity Address, Address Line One | One Commerce Square |
| Entity Address, Adress Line Two | 2005 Market Street, 39th Floor |
| Entity Address, City or Town | Philadelphia |
| Entity Address, State or Province | PA |
| Entity Address, Postal Zip Code | 19103 |
| City Area Code | 267 |
| Local Phone Number | 866-0311 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.0001 Par Value Per Share |
| Trading Symbol | PASG |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Entity Central Index Key | 0001787297 |
| Amendment Flag | false |
