Keita had been Liverpool's primary transfer target during the current transfer window, only for Leipzig to repeatedly rebuff the club's advances for the 22-year-old.
However, the Reds have now clinched a deal that will see Keita move to Anfield for £48m plus a premium in order to secure the transfer a year in advance, and Henderson is looking forward to playing alongside the Guinea international.
"If you play for top teams you are going to sign good players. I have seen Naby play quite a few times and he looks a top, top player," he told reporters.
"There have been a lot of transfer rumours over the summer and thankfully we ended up doing the business. Okay, he comes next year, but I am sure the club are delighted to get him because he will be a real addition to the squad and will hopefully help us over the next few years."
Keita scored eight goals in 31 appearances last season to help Leipzig finish as runners-up in the Bundesliga.