The aim of this study was to evaluate the impact of feeding ethyl-cellulose rumen-protected methionine on the performance and liver function of dairy cows during the periparturient period and early lactation. Sixty multiparous Holstein were used in a block design and assigned to either a control diet or Met-supplemented (Mepron, Evonik Nutrition & Care GmbH, Germany) diet. Mepron was supplied from −28 to 60 d relative to parturition at a rate of 0.09% and 0.10% of DM during the prepartum and postpartum period, respectively. That rate ensured that the ratio of Lys to Met in the MP was close to 2.8:1. Blood samples from 15 cows per treatment were collected at −30, −14, 1, 7, 21, 30 and 60 d relative to parturition. The statistical model included the random effect of block and fixed effect of treatment, time and interactions. Cows fed Met had intakes of dry matter that were 1.2 kg/d greater during the prepartum period. Compared with control, during the fresh period (1 to 30 DIM) feeding Met increased DMI by 1.65 kg/d, milk yield by 4.1 kg/d, fat yield by 0.17 kg/d, milk protein yield by 0.2 kg/d, 3.5% FCM by 4.3 kg/d and ECM by 4.4 kg/d. Although Met supplementation increased milk protein content by 0.16% units compared with control during the fresh period, no differences were observed for milk fat, lactose, and MUN concentration. During the high production period (31 to 60 DIM), compared with control cows, feeding Met increased DMI by 1.45 kg/d and milk yield by 4.4 kg/d. Met also increased fat yield by 0.19 kg/d, milk protein yield by 0.17 kg/d, 3.5% FCM by 4.7 kg/d and ECM by 4.8 kg/d. Among the biomarkers analyzed, Met led to overall lower (P = 0.01; 15.1 vs 22.9 U/L) γ-glutamyl transferase. For cholesterol, a treatment × time (P = 0.07; 4.0 vs 3.5 mmol/L) was observed due to a greater increase over time in Met-fed cows. Aspartate aminotransferase, alkaline phosphatase and bilirubin were not affected by Met. Liver tissue triacylglycerol concentration also was not affected by Met. In conclusion, ethyl-cellulose rumen-protected methionine supplementation improved dairy cow performance during the prepartum and through the peak of lactation.