| Document and Entity Information | Feb. 04, 2024 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001746473 |
| Document Type | 8-K |
| Document Period End Date | Feb. 04, 2024 |
| Entity Registrant Name | PLIANT THERAPEUTICS, INC. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-39303 |
| Entity Tax Identification Number | 47-4272481 |
| Entity Address, Address Line One | 260 Littlefield Avenue |
| Entity Address, City or Town | South San Francisco |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94080 |
| City Area Code | (650) |
| Local Phone Number | 481-6770 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.0001 per share |
| Trading Symbol | PLRX |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
