I assume it's based on who's the max level

Think is alwas max lvl hero of this party too. Not time to test.

With actual mechanics, normally first hero always lvl up faster, uless you leave him/her/it into a fleet or a system with very low production.

I tested it, and it's not the hero with the highest level. My theory is, that currently, the first recruited hero of a political partie is always the senator.  But this doesn't explain, why my heroes switched once. 

Aimer wrote:

I tested it, and it's not the hero with the highest level. My theory is, that currently, the first recruited hero of a political partie is always the senator.  But this doesn't explain, why my heroes switched once. 

For me too, The first hero is the one that become senator (I had more with more levels and they didn't switch) so still I have no idea why yours switched, Could be maybe that your hero went to coldown or were injured? I don't know...

^thats interesting! Just force a defeat in a space battle wioth the current hero. maybe it works.

I also experienced hero switching on one occasion, it went from lvl 25 vodyani to lvl 3 amoeba, I was not thrilled and it never changed back.

I also suspect that it might be connected with the hero being disabled.

Aimer wrote:

^thats interesting! Just force a defeat in a space battle wioth the current hero. maybe it works.

 Does not work. The hero keeps the senator slot, despit being injured.

Was there a change in government type or political party?  I can't fathom what else might affect that...

koxsos wrote:

I also experienced hero switching on one occasion, it went from lvl 25 vodyani to lvl 3 amoeba, I was not thrilled and it never changed back.

I also suspect that it might be connected with the hero being disabled.

I've had a hero switch once, iirc the main hero "lost" the senate seat to a secondary hero. I was using the main as fleet general and the second one as system administrator:

Could this be linked with the number of "senator skills" that the heroes have taken ? I.E. the hero with most skills which have effects on senate takes the political lead ?

As of current patch situation (and couple previous ones), it counts of "point invested into senator skills". = this means if both have equal number of "senate effect skills" one who has more points invested (rank 2s for instance) gets to be a senator.

You won't believe how much I thank you for this awnser!