In peace and conflict research the study of peace agreement implementation has often focussed on the duration of peace. This however risks overlooking the implementation of the peace agreement as a whole. Simultaneously, the relationship between biased versus neutral mediators and the degree of agreement implementation has not been systematically investigated. This study addresses this gap by asking: how does biased mediation affect the implementation of peace agreements? I apply the logic of theories on artificial incentives for peace (Beardsley 2008) and argue that biased mediators will create and use more temporary incentives to induce the warring parties towards a negotiated settlement. Once a peace agreement is signed and the mediator’s influence wanes, it is argued that these artificial incentives ultimately result in reduced momentum for implementation and a lower degree of implementation overall. This leads to the expected hypothesis that if a mediator is biased peace agreements will be implemented to a lower degree. Using the methods of structured, focussed comparison and process tracing, this paper will compare the mediation and implementation processes in the Tajikistan and Burundian civil wars. The findings display partial support for the hypothesised causal mechanism, although the hypothesis overall is not supported.