"Guidelines adopted unanimously. EU27 firm and fair political mandate for the Brexit talks is ready," said Tusk via his Twitter account during a meeting of the European Council.
The guidelines outline the continuation of relations between the EU and Britain until determination of its debt to the EU and resolution of the border issue between the U.K. and Ireland.
After Brexit, the EU also wants guarantees for EU member state citizens living or working in the U.K., as well as for their welfare benefits and rights.
"EU27 unity on Brexit is unique. I'm confident it won't change," said Tusk. "Only by remaining united can we conclude the talks."
Before the meeting in Brussels, Belgian Prime Minister Charles Michel voiced his concerns about the guidelines, saying the EU should not let Britain manipulate it.
"Maybe the UK government would do its best to divide the 27 countries, which is a trap we should avoid," he said.
The U.K. government last month officially began the process of leaving the EU, after 52 percent of British voters chose to leave the EU in a June 2016 referendum.