Berlioz finally appears in catalogue as composer (5)
I believe the answer is:
liszt
'composer' is the definition.
(Franz Liszt)
'berlioz finally appears in catalogue' is the wordplay.
'finally' suggests the final letters.
'appears in' indicates putting letters inside.
'catalogue' becomes 'list' (a catalogue is a list of items).
The final letter of 'berlioz' is 'z'.
'z' going inside 'list' is 'LISZT'.
'as' is the link.
(Other definitions for liszt that I've seen before include "Pianist and composer Cockneys associate with Brahms" , "music writer" , "Hungarian composer,d. 1886" , "Composer of the Hungarian Rhapsodies" , "Franz . . . . ., great Hungarian composer" .)