The purpose of this study is to assess the safety, pharmacokinetics (PK), pharmacodynamics (PD), immunogenicity and activity of RO7790121 in participants with advanced metabolic dysfunction-associated steatohepatitis (MASH) fibrosis.

Inclusion Criteria:

• Body mass index within the range of >= 25 and <=45 kilograms per square meter (kg/m^2)
• MASH with fibrosis score of F3 or F4 confirmed by transient elastography measurement >=12.0 kPa and <=25.0 kPa
• Agreement to adhere to the contraception requirements

Exclusion Criteria:

• Weight gain or loss >5% in the 3 months prior to baseline or >10% in the 6 months prior to baseline
• Bariatric surgery within 1 year prior to baseline
• Current signs or prior history of decompensated liver disease
• Complications or clinical evidence of portal hypertension
• Lack of peripheral venous access
• Other causes of liver disease based on medical history and/or centralized review of liver histology
• History of liver transplantation
• Current or prior history of hepatocellular carcinoma (HCC)
• Uncontrolled hypertension
• Concomitant Type 1 diabetes, or Type 2 diabetes with HbA1c >10%
• History of malignancy within 5 years prior to screening, with the exception of malignancies with a negligible risk of metastasis or death
• Current, significant alcohol consumption or a history of significant alcohol consumption for a period of more than 3 consecutive months any time within 1 year prior to screening
• Initiation of a medication of an antidiabetic, weight loss, lipid-modifying or anti-depressant drug class
• Active tuberculosis requiring treatment within the 12 months prior to baseline
• History of organ transplant