"The announcement came in tweets from the current council president, Herman Van Rompuy, at an EU summit.
Ms Mogherini, a centre-left politician, is Italy's foreign minister. She will replace the UK's Catherine Ashton. Mr Tusk, Poland's centre-right prime minister, has been Polish leader since 2007. He will chair EU summits.
The full-time appointments mean that the EU's three top jobs are now filled. Mr Tusk and Ms Mogherini will work closely with the new European Commission President, Jean-Claude Juncker.
Mr Tusk, 57, will serve for two-and-a-half years (renewable), starting on 1 December. Ms Mogherini's term, starting on 1 November, is five years.
Mr Van Rompuy called Mr Tusk "one of the veterans of the European Council", the grouping of EU government leaders. He is the only Polish prime minister to have been re-elected since the collapse of communism in 1989. Mr Van Rompuy praised "the determined and confident way he has steered Poland through the economic crisis, and managed to maintain steady economic growth". As a student Mr Tusk was active in the Solidarity anti-communist movement.
Mr Van Rompuy said Mr Tusk would face three major challenges: the stagnating European economy, the Ukraine crisis and "Britain's place in Europe". He said the EU leaders were convinced that Ms Mogherini, 41, "will prove a skilful and steadfast negotiator for Europe's place in the world". He noted Italy's "long-standing tradition of commitment to the European Union".
Ms Mogherini, speaking fluent English, later said "the challenges are huge... all around Europe we have crises - on European soil, in Ukraine, and starting from Iraq and Syria, going to Libya".
On arrival at the summit the European Parliament President Martin Schulz, a Socialist, spoke warmly of Ms Mogherini, calling himself a "fan". It was a strong indication that she would be a popular choice among MEPs. The parliament's approval is required for all 28 members of the new Commission, and the EU foreign policy chief, officially called the High Representative, is also a vice-president of the Commission.
Baroness Ashton, a centre-left UK politician, has been in the job since 2009. The High Representative runs the EU External Action Service (EEAS). Italy's centre-left Prime Minister Matteo Renzi pushed hard for Ms Mogherini to get the job.
However, last month the EU failed to get a consensus on her candidacy, as the Baltic states and Poland saw her as inexperienced and too soft on Russia. She has only been Italian foreign minister since February. "
Link to BBC