Leading journo travelled back across it (6)
I believe the answer is:
editor
'leading journo' is the definition.
(leading journalist)
'travelled back across it' is the wordplay.
'travelled' becomes 'rode' (I've seen this before).
'back' is a reversal indicator.
'across' indicates putting letters inside.
'rode' in reverse letter order is 'edor'.
'edor' placed around 'it' is 'EDITOR'.
(Other definitions for editor that I've seen before include "Rag worker" , "Redo it and become head of publication" , "Triode (anag.)" , "Someone in the rag trade" , "Paper head" .)