Mr Plunkett will also help to represent consumers in the energy and postal markets as well as its influential policy work under the themes of families, welfare and work; consumer policy, citizenship and democracy.
He previously headed up the charity's consumer policy and campaigns team. Prior to this he was director of policy at the Resolution Foundation and has worked at number 10.
Gillian Guy, chief executive at Citizens Advice, said: “For two in three of our clients we are able to solve their problem outright but, for the others, there are often more systematic issues which stand in the way of resolving an issue.
“That's why our policy work is so important. By showing government, businesses and local authorities the challenges people are facing, and proposing workable fixes, we can stop problems in their tracks and prevent more people from experiencing them in future."
Mr Plunkett said: "I'm incredibly proud to work alongside the fantastic policy and campaigns staff from across the Citizens Advice service.
"Citizens Advice has a long history of helping people overcome problems in their lives and, in our policy work, we take insights from these conversations to fix the root causes of these problems.”