If I have an external drive that has both my photos and catalog file, can use this drive and work in Lightroom on both a Mac and PC?
Basically, I have a desktop running Lightroom CC and a MacBook Pro with Lightroom CC (both are the latest 2015 subscription version). I want to be able to use the Mac to work on pictures from external drive when traveling, but the desktop when I'm home.
Can this be done or are the catalog files / path different moving between the two operating system platforms?
Yes, it is possible and this is what most of the people does, It is the most effective and less time consuming process to work on Lightroom on multiple systems with updated edits, however there is only one issue when you connect external hard drive to the Mac, it will see it by its name like Seagate Or WD but in Windows when you connect the external hard drive it will assign a drive letter to it like E, F etc. therefor Lightroom will get confused on one of the systems where it will not able link the original images to the Catalog.
So either you have two Windows system Or two Mac machine for smooth process.