The Omnicom-owned agency, which has offices in Brussels, Paris and Berlin, plans to boost its UK offer in light of Brexit.
Wallace (pictured) will be based in London and told PRWeek: "UK-based companies will need even more help in the future now that the UK government will not be sitting in the room when EU decisions are made."
The public affairs and comms agency has more than 70 staff across its business.
GPlus managing partner Daniel Brinkwerth said Wallace would add "real strength to our offer". "Emily’s appointment will ensure that we can provide post-Brexit support and analysis to existing and new clients as businesses look at how and in which areas the UK will diverge from the EU," he added.
Wallace added: "With Brexit around the corner, I’m excited to be joining GPlus to lead and develop their UK advisory services, as well as make a significant contribution to the success of the whole company".
"GPlus has a formidable reputation as a fully integrated agency, working seamlessly across its European offices to best support its clients. UK-based companies will need even more help in the future now...I believe with my colleagues in Brussels, Paris and Berlin that we are ideally placed to really help those companies protect their interests."
Wallace, a highly regarded public affairs professional who has served as deputy chair of the APPC, recently conducted a review into the public affairs and the future direction of the self-regulatory body APPC.
Since then, she has come out against a proposed merger between the PRCA and APPC, saying she was "stunned" that a formal proposal was put forward.
"Maybe there are some in our industry that are happy to see the demise of the APPC, happy to see a weakened self-regulatory regime, but without an independent self-regulatory body, we surely make the likelihood of further statutory regulation more likely," she said in a comment piece.