This song is in the Key of C Major and follows the normal C progressions.
My notation will be CAPS for MAJOR and lowercase for minor.

ex:  C = C MAJOR
     e = e minor


Time 6/8
Intro:  |   C    |    a    |

all but last verse (I'll include the first verse):
C                   a
I heard there was a secret chord
C                   a
That David played and it pleased the Lord
F                   G                   C
But you don't really care for music do ya?


C                     F           G
It goes like this the fourth, the fifth,
a               F
The minor fall, the major lift, 
G                   e              C
The baffled king composing hallelujah
C     a     a    C
Hallelujah, Hallelujah
C     a     C     a    G    C
Hallelujah, Hallelu - oo -- jah


The rest follows that same pattern except at the very end where he repeats the Hallelujah lines twice.
Hope you enjoy this song too.