Question

Which is correct grammar? "He has already come." or "He has already came"?

Answer 1

He has already come.

Explanation:

Sometimes the insertion of an adjective (in this case "already") makes the verb structure more difficult to see.

If the sentence is re-stated as:
`color(white)("XXX")`He already has come.
it is easier to see the present perfect tense. (Note that despite its name, the "present perfect" is a past action tense).

There are 3 (main, see note below) past tenses (in English):

#{: ("simple past:","independent action completed in past", " | ","He came."), ("present perfect:","action completed before now"," | "," He has come."), ("past perfect:","action completed before some other action in the past"," | ","He had come.") :}#

In addition to these main forms there are also past progressive forms for ongoing actions in the past:

#{: ("simple past progressive"," | ","He was coming."), ("present perfect progressive"," | ","He has been coming."), ("past perfect progressive"," | ","He had been coming") :}#

Answer 2

He has already come.

Explanation:

Come is third form of verb. That is 1. Come. 2. Came and 3. Come.
In present perfect tense the third form of verb to be used.