Is as long as a conjunction?

Yes, it is a compound conjunction with two different usages.

1) until some indefinite point in the future, e.g. for as long as I live

- the following clause has a verb in the present tense

2) on the condition that, e.g. as long as you are careful

- again, the following clause uses a present-tense verb

The second meaning is a version of the compound conjunction "so long as" which is less used.