事(こと)になるIt will end up being, It is the result of, It has been decided that

ことになる is an expression that combines the nominalizing use of こと (creating a noun-phrase), with the case marking particle に, and the う - Verb なる 'to become'. This expression can be translated as 'to become (A)', but has the nuance that someone/thing caused (A) to become that way. Due to this, it may also be translated as 'it has been decided that (A)', or 'it will end up being (A)'.

ことになる is primarily used with verbs and い-Adjectives in their attributive form. It may also be used with な-Adjectives followed by な.

The 'it has been decided that (A)' meaning only applies to verbs, as only verbs will be enacted by someone/thing.

Fun Fact

This structure is a good example of why なる is often viewed as the intransitive form of する. する conveys that someone is performing an action (transitive), while なる implies that something is the result of an action (intransitive). This is why the (A) phrase in ことになる is usually determined to have been decided/performed by someone else, while still focusing on exactly 'what' (A) became.