Protein phosphatase 1 (PP1) inhibitors play a role in tumor progression through different mechanisms. Protein phosphatase 1 regulatory subunit 14D (PPP1R14D) is an inhibitor of PP1. However, the role of PPP1R14D in tumors and its mechanism of action are largely unknown. The purpose of the present study was to investigate the expression, function and mechanism of PPP1R14D in lung adenocarcinoma (LUAD). In the present study, GEPIA database analysis and immunohistochemistry demonstrated that PPP1R14D was highly expressed in LUAD tissues and that the expression of PPP1R14D in LUAD was negatively correlated with the age of patients and positively correlated with the 8th American Joint Committee on Cancer staging among patients. In addition, Kaplan‑Meier Plotter database analysis showed that PPP1R14D expression was associated with lower survival rates in patients with LUAD. PPP1R14D knockdown significantly inhibited LUAD cell proliferation, migration and invasion and induced LUAD cell arrest at the G1 phase of the cell cycle. Mechanistic analyses revealed that PPP1R14D knockdown may inhibit cell proliferation, migration and invasion by inactivating PKCα/BRAF/MEK/ERK pathway signaling and its downstream key proteins c‑Myc/Cyclin E1‑CDK2 and MMP2/MMP9/Vimentin. Moreover, knockdown of PPP1R14D suppressed tumor growth in vivo. All these results showed that PPP1R14D plays an important role in LUAD tumorigenesis and may serve as a potential prognostic factor and therapeutic target in LUAD.