The Global Radio-owned station will move its LBC News 1152 presenters Hartigan and Hosken to a weekday 4pm-7pm drivetime slot from January 14.
Jeni Barnett, the broadcaster's Sunday afternoon food and drinks programme host, will take on the weekday 1pm-4pm show from January 7.
James Max, currently presenter of the station's Saturday 'The Fine Things in Life' and 'Business Matters' programmes, will now front a new breakfast show between 5am and 7am on Fridays and from 6am to 8am on Saturdays.
The changes do not affect Alison Bell and Paul Ross' status as fill-in presenters at LBC 97.3, while the station's 'Nightly News' slot will now be broadcast at 7pm, before Nick Abbot's evening programme.
Jonathan Richards, programme director at LBC 97.3, said: "James and Petrie will bring Londoners a fast-moving round up of the day's news while inviting listeners to comment on what's been happening.
"James Max is an emerging talent and his early breakfast shows will display not only his business expertise but his engaging personality."