This study will look into testing a new medicine called NNC0363-1063 which may be used to treat people with diabetes. The study consists of three parts: Part 1 is a single ascending dose (SAD) study that comprises two subtypes: Part 1A conducted in healthy participants and Part 1B conducted in participants with type 1 diabetes (T1D). This study part will last for about 1½ to 5½ weeks. Part 2 is a proof-of-principle (PoP) study part conducted in participants with T1D and will last for about 3½ to 8½ weeks. Part 3 is a meal test multiple dose study part conducted in participants with T1D and will last for 7 to 11 weeks.

Inclusion Criteria:

Part 1A SAD (healthy participants)

• Male or female of non-child bearing potential. Non-child bearing potential being defined as surgically sterilised (i.e. documented hysterectomy, bilateral salpingectomy or bilateral oophorectomy) or being postmenopausal (defined as no menses for 12 months without an alternative medical cause) prior to the day of screening.
• Age 18-64 years (both inclusive) at the time of signing the informed consent.
• Body mass index between 18.5-29.9 kilogram per square metre( kg/m^2) (both inclusive) at the day of screening.
• Considered to be generally healthy based on the medical history, physical examination, and the results of vital signs, electrocardiogram and clinical laboratory tests performed during the screening visit, as judged by the investigator.

Part 1B SAD, Part 2 PoP and Part 3 Meal test (participants with T1D)

• Male or female of non-child bearing potential. Non-child bearing potential being defined as surgically sterilised (i.e. documented hysterectomy, bilateral salpingectomy or bilateral oophorectomy) or being postmenopausal (defined as no menses for 12 months without an alternative medical cause) prior to the day of screening.
• Age 18-64 years (both inclusive) at the time of signing the informed consent.
• Body mass index between 18.5-29.9 kg/m^2 (both inclusive) at the day of screening.
• Diagnosed with type 1 diabetes mellitus greater than or equal to( ≥)1 year prior to the day of screening.
• Considered to be generally healthy (except for mild conditions under stable treatment associated with type 1 diabetes mellitus) based on the medical history, physical examination, and the results of vital signs, electrocardiogram and clinical laboratory tests performed during the screening visit, as judged by the investigator.

Exclusion Criteria:

Part 1A SAD (healthy participants)

• Male of reproductive age who, or whose female partner(s), is not using an adequate contraceptive method.
• Any condition, which in the investigator's opinion might jeopardise participant's safety or compliance with the protocol.

Part 1B SAD, Part 2 PoP and Part 3 Meal test (participants with T1D)

• Male of reproductive age who, or whose female partner(s), is not using an adequate contraceptive method.
• Any condition, except for mild conditions under stable treatment associated with type 1 diabetes mellitus, which in the investigator's opinion might jeopardise participant's safety or compliance with the protocol.

According to the Novo Nordisk disclosure commitment on novonordisk-trials.com

Part 1 SAD and Part 3 Meal test are double-blind study parts. Sponsor staff involved in the clinical trial is masked according to company standard procedures. Part 2 is open-label study part.