Westerwelle was due to meet President Jalal Talabani, Prime Minister Nuri al-Maliki, Foreign Minister Hoshyar Zebari and parliament speaker Osama al-Nujaifi, the foreign ministry in Berlin said in a statement.
"We want to send a signal that we support the stabilisation of Iraq and the continuation of the democratic process," Westerwelle said, according to a statement released by the ministry.
An official in Nujaifi's office told AFP on condition of anonymity that Westerwelle would be hosted by the speaker and the Iraqi parliament on Saturday, but the rest of his schedule could not immediately be confirmed.
Another parliamentary official confirmed the upcoming meeting in Iraq's Council of Representatives.
Westerwelle is also due to meet with Christian leaders, the German foreign ministry said, after a series of attacks on Iraq's minority Christian community, in particular a siege on a Baghdad church left 44 worshippers and two priests dead, sparked international outrage.
He was being accompanied by members of Germany's Bundestag and representatives of German businesses, the statement from Berlin said.
Germany will in particular be looking to deepen economic engagement with Iraq as the war-ravaged country seeks to rebuild its moribund economy and crumbling infrastructure.
In particular, a bilateral deal on the protection of investments is expected to be signed with Industry Minister Fawzi Hariri, with the new accord helping improve "economic and legal conditions for German companies" working in Iraq, Westerwelle said in the statement.
Berlin hosted a two-day investment conference for Iraq in November 2009 in a bid to promote trade between the two countries.