(1) Background: The 2016 WHO classification of Tumors of the Central Nervous System brought an escalating research interest in lower-grade gliomas (LGGs). This study aims to establish individualized prognostic nomograms to predict the overall survival (OS) and cancer-specific survival (CSS) of patients with LGGs;(2) Methods: We searched the Surveillance, Epidemiology, and End Results (SEER) database for adult patients diagnosed with LGGs from 1998 to 2016. The patient data set selected from SEER was randomly divided into training and validation data sets at a ratio of 7:3. The significant prognostic factors were identified by using multivariate regression models in the training dataset. Then OS and CSS nomograms were developed and internally validated;(3) Results: After the inclusion and exclusion criteria set, a total of 12,630 patients were enrolled in our research. The prognosticators for OS contained age, sex, race, marital status, surgery, radiotherapy, chemotherapy, tumor size/site, laterality, WHO grade, while only chemotherapy among the 11 indicators mentioned above was not related to CSS. The c-indexes of OS and CSS of the validation cohort were 0.749 and 0.761, respectively. The calibration curve plots showed that the predicted probability of 3-, 5-, and 8-years survival rates corresponded well with the actual observed OS and CSS rates;(4) Conclusion: The present study using the SEER database constructed and internally validated prognostic nomograms to predict the OS and CSS of patients with LGGs. The nomograms showed perfect predictive abilities and may be useful clinical tools for decision aids and better supporting patient counselling.