Toxic and carcinogenic arsenic is a common environmental pollutant that poses a serious threat to human health through contaminated water and plant-based foods. Efflux of arsenic by the membrane transporters of the ACR3 family is an ancient detoxification pathway widely distributed among bacteria, archaea, fungi, and plants, except angiosperms. Plant ACR3 proteins remain largely uncharacterized. Here we show that, similar to bacterial and fungal orthologues, ACR3 from the liverwort Marchantia polymorpha (MpACR3) acts as a plasma membrane arsenite/proton antiporter that confers increased resistance to both arsenite and arsenate. We also uncover that MpACR3 possesses an arsenic sensing domain that regulates MpACR3 trafficking and function. We will provide detailed molecular insight into how MpACR3 senses the presence of arsenic in the cytoplasm and how this effects MpACR3 sorting. The arsenic-sensing domain is common among plant ACR3 transporters and therefore represents a plant-specific adaptation to arsenic poisoning via the rapid accumulation of ACR3 protein at the plasma membrane.