The conglomerate said late Thursday it has received approval from the FCC for its request for the "transer of de jure control" of the satellite-radio firm, and it expects the complete transfer to occur within 60 days.
Liberty intends on converting preferred securities and debt in order to obtain enough shares to own more than 50 percent of Sirius, and FCC said it expects that to happen before the 60 days are up.
Liberty has been buying shares for several months and is already very close to the 50-percent threshold. The buying spree has been a catalyst for a surge in Sirius XM's stock price, which closed Thursday at $3.08, up 47 percent in six months.
Liberty has already replaced Mel Karmazin as CEO, installing James Meyer as Sirius XM's interim chief, and it has suggested that after it takes control of the radio company it will spin it off.
In connection with Irving Azoff stepping down as CEO of Live Nation on Monday, Liberty purchased 1.7 million shares of Live Nation stock from Azoff, increasing its stake to 26.4%.