adverb
Used for something that happens after a short passage of time, often in narrative sequence. It sounds a little more written or storytelling-like than very plain すぐ or まもなく.
空が暗くなり、やがて雨が降り出した。
The sky grew dark, and before long it began to rain.
Soon the train pulled into the platform.
adverb
Used before an amount of time or quantity to mean that it is approaching that amount. This use is more limited than the basic temporal sense.
この町に来て、やがて十年になる。
It has been nearly ten years since I came to this town.
adverb
eventually; finally; in the end
Marks the outcome reached after time, change, effort, or a sequence of events. Compared with ついに, やがて is less emphatic and more about natural progression over time.
何度も失敗したが、やがて成功した。
He failed many times, but eventually succeeded.
小さな店は、やがて全国に知られる会社になった。
The small shop eventually became a company known throughout the country.