The acquisition close follows the Letter of Intent executed on 22 December 2010, and the SPA announced on 23 February 2011.
As previously reported, the consideration for the transaction is €12.8m with a three year earn-out opportunity of up to €5.2m.
On Assignment utilized a combination of cash on-hand and borrowing under its senior credit facility.
On Assignment president and CEO Peter Dameris said Valesta will not only enhance their service offering in an attractive end market within Life Sciences, but it will also expand their international footprint.
"On Assignment is focused on our growth strategy to reach one billion dollars in revenue over the next five years. The acquisition of Valesta positions us well to continue toward our revenue and profitability goals," Dameris said.