The €1.8 billion ($1.9-billion) deal will see ArcelorMittal join forces with Italy's Marcegaglia to snap up the heavily indebted company, one of the most polluting industrial sites in Europe.
Ilva currently has 14,000 employees, of whom 11,000 work at its site in Taranto.
ArcelorMittal, in its statement, undertook "to keep at least 10,000 employees for the entire duration of the industrial plan according to the outcome of negotiations with the unions".
After news first leaked of the takeover, hundreds of employees at Ilva's site in the northwestern city of Genoa staged a protest earlier this month.
Ilva's Taranto site in southern Italy is at the centre of a huge legal case in which experts cited by prosecutors have charged that 11,550 people have died from toxic emissions in seven years.
Italian bank Intesa Sanpaolo will join the consortium before the deal is closed.
The offer includes plans to invest €2.4 billion in Ilva, with funds earmarked for upgrading industrial equipment and improving environmental standards.
"Ilva is an important strategic acquisition for ArcelorMittal," said Aditya Mittal who heads ArcelorMittal's European operations.
"It provides us with a significant production presence in a country in which we have no primary steelmaking capacity, and is complementary to our existing European business."