Yes one can continue to work with Porphyria, depending on the type you have this will determine the field. If you have a cutaneous porphyria you wouldnt be able to work outside for example as a landscaper or gardener. There are some newer types of clothing which have been developed however these just reduce the risk and dont necessarily eliminate it.
So having said that its possible to work whilst having Porphyria, not every field will be suitable and one would need to take into account the type of work, the environmental conditions and the type of Porphyria to determine that.
A perfect example is I trained as a hairdresser and had to stop because of the reaction to the chemicals, having my hands in water which affected my skin severely.
Many instances the stress of a particular job will be too high and trigger an attack, often times one may have to change careers in order to find more suitable ones.
I would estimate that there are perhaps 25% of people who have Porphyria can work in any type of field, if they have an active porphyria this may affect the percentage, including the fact that there are still many who are undiagnosed with porphyria.