The prognostic signatures play an essential role in the era of personalised therapy for cancer patients including lung adenocarcinoma (LUAD). Long noncoding RNA (LncRNA), a relatively novel class of RNA, has shown to play a crucial role in all the areas of cancer biology. Here, we developed and validated a robust LncRNA-based prognostic signature for LUAD patients using three different cohorts. In the discovery cohort, four LncRNAs were identified with 10% false discovery rate and a hazard ratio of $>$ 10 using univariate Cox regression analysis. A risk score, generated from the four LncRNAs’ expression, was found to be a significant predictor of survival in the discovery and validation cohort (p = 9.97 $\times 10^{−8}$ and 1.41$\times 10^{-3}$, respectively). Further optimisation of four LncRNAs signature in the validation cohort, generated a three LncRNAs prognostic score (LPS), which was found to be an independent predictor of survival in both the cohorts ( p = 1.00 $\times 10 ^{−6}$ and 7.27 $\times 10^{−4}$, respectively). The LPS also significantly divided survival in clinically important subsets, including Stage I ( p = 9.00 $\times 10^{−4}$ and 4.40 $\times 10^{−2}$, respectively), KRAS wild-type (WT), KRAS mutant ( p = 4.00 $\times 10^{−3}$ and 4.30 $\times 10^{−2}$, respectively) and EGFR WT ( p = 2.00 $\times 10^{−4}$). In multivariate analysis LPS outperformed, eight previous prognosticators. Further, individual members of LPS showed a significant correlation with survival in microarray data sets. Mutation analysis showed that high-LPS patients have a higher mutation rate and inactivation of the TP53 pathway. In summary, we identified and validated a novel LncRNA signature LPS for LUAD.