Vincenzo Oliva's answer – domi militiaeque and variations thereof – is certainly the most established expression. I found another one that I also liked, it is found in Livy's Ab urbe condita (6.18), citing an argument presumably made by M. Manlius Capitolinus to rouse the Plebeians, talking about the danger that he will be carried off to prison or worse:
Bene facitis quod abominamini. Di prohibebunt haec; sed nunquam propter me de caelo descendent; vobis dent mentem oportet ut prohibeatis, sicut mihi dederunt armato togatoque ut vos a barbaris hostibus, a superbis defenderem civibus.
Great of you that you act all appalled, saying: “The Gods will prevent this!” But the Gods won't descend from heaven for my sake; they can only give you the courage to prevent it, just like they gave me the courage to defend you, wearing my armour and wearing my toga, from foreign enemies and from citizens who deem themselves above others.
Armatus togatusque (as cnread points out in his comment, the form armato togatoque is in the dative case agreeing with mihi) does not exactly mean “in war and peace,” it literally means “armed and wearing a toga” or, more freely: “equipped to go to war / appropriately dressed to engage in business and politics.” The point is that the toga was the Roman men's civilian dress. Georges actually mentions this quote, translating it as „im Kriegs- und Friedensgewande“, that is, in warlike and peaceful garb.
I think it lends itself to metaphorical use, but it is not a prepositional phrase like in bello, so it has to be adapted to the sentence and might quickly look awkward when not talking about people. For example:
- Caesar armatus togatusque summa aequitate res gerebat. (Looks fine, I think.)
- Galli Romam armatam togatamque numquam imparatam offenderunt. (Looks a little weird.)
- Triremes Athenienses armatae togataeque omnibus a Graecis laudabantur. (OK, that is weird.)
Just as the toga signifies peace, so does the sagum (a soldier's cloak) signify war. Sagatus is also an attested word, so one might form sagatus togatusque.
Searching on Google for sagato togatoque (and vice versa, and other forms), I found a few hits; all of them not looking particularly classical though, but I also like that combination.