He worked for the UN for 30 years – in assignments in Haiti, Pakistan, Afghanistan, Iran, Iraq and Sierra Leone, among others.[3] When serving at the United Nations Integrated Peacebuilding Office in Sierra Leone (UNIPSIL) as the highest UN representative in Sierra Leone (Executive Representative of the Secretary-General – ERSG), he came into conflict with the government over the implementation of the Lomé Peace Agreement, police arming and the forthcoming presidential elections. In 2012, he was asked to leave the country.[4][5]
In 2001 Schulenburg accused Pino Arlacchi, the Director General of the UN in Vienna and of the UN Office for Drug Control and Crime Prevention, in a confidential letter that was later leaked to the press, that the office under Arlacchi's leadership suffered from fear, intimidation and a general lack of transparency. An official UN investigation later confirmed the accused mismanagement practices.[6]
In 2009 Schulenburg put himself at risk in Sierra Leone to save 22 youths of the opposition[7] from being lynched by a large crowd that was attacking the opposition's headquarters.[8]
Since his retirement from the UN, Schulenburg worked as an advisor[9] and as a publicist.[10][11] In 2017, he published his book On Building Peace – Rescuing the Nation-State and Saving the United Nations.[12]
In 2024 he signed a "joint declaration" with Harald Kujat in support of China's supposed "peace plan", arguing that Ukraine "can no longer win the war, even with more weapons."[14]