The Russian leader claimed the so-called referendums in Donetsk, Luhansk, Kherson and Zaporizhzhia - which have been branded a sham in the West - where the "will of millions of people".
Documents were signed by Putin and the Russian-appointed leaders of the four regions, effectively declaring them Russian territory.
Rebuilding land
Putin said the land being seized would benefit from Russia rebuilding "the ruins in towns and villages" - despite the fact it was Russia that caused the destruction.
Attack on West
A large majority of the speech was taken up by Putin ranting against the West, making unfounded claims, including Britain being part of an apparent plan to destroy parts of the Nord Stream pipeline
Western officials are waging a "hybrid war" against Russia and want to colonise it
Energy prices
Putin also claimed Russia was not to blame for soaring global energy prices, saying instead this is a result of "many years of wrong policies".
"There are four new regions of Russia," Putin said in a televised ceremony from the Kremlin in Moscow, according to a translation.
"The results are known, well known," Putin said, referring to the series of votes that Ukraine and Western governments say breached international law. He claimed the results were due to the will of millions of people, saying they had the right to self-determination.
The territory being seized more than seven months into the Kremlin's war consists of two pro-Russian "republics" in Luhansk and Donetsk in the east and in Kherson and Zaporizhzhia in the south. It is thought to make up roughly 18% of Ukraine's land, although the precise details of the boundaries were not immediately apparent.
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