Last season's Championnat runners-up have bolstered their armoury ahead of their quest to go one step further with the twin capture.
Cameroon international Song arrives in Lens on a free transfer from West Ham after spending the latter of the past season on loan at Cologne.
Song has signed a four-year contract and the club's sporting director Patrice Bergues was delighted with the acquisition.
With Jean-Guy Wallemme and Valerien Ismael leaving the club, Bergues was keen to secure an experienced stopper.
"It was essential to find a central defender of great experience and someone who is able to direct the rearguard," said Bergues. "This is what we have done."
The Indomitable Lions' skipper was tempted by the prospect of linking up with both Bergues, who he knows from his time at Liverpool, and also coach Joel Muller, who was his boss at Metz.
Striker Keita arrives from Lorient on a one-year loan deal, although Lens have the option to buy the Mali international next summer.
Keita had been keen to wrap up his switch and will be perceived as a replacement for livewire striker El Hadji Diouf, who is joining Liverpool.
However, Lens are still waiting to tie up the loose ends of their £3 million swoop for rangy hit-man Dagui Bakari from Lille.
Bakari has yet to successfully complete a medical with Lens awaiting the results of an MRI scan.
Meanwhile, goalkeeper Guillaume Warmuz is expected to stay at Felix-Bollaert for a further season, unless an offer in the region of ‚é¼350,000 is received.
Bruno Rodriguez, though, is certain to leave Lens in his quest for first team football but has already witnessed possible moves to Montpellier and Bastia fall through.
