The period romp launched with 9.3m total viewers on January 19, with the first three episodes averaging 6.3m in overnights.
BBC One Controller Charlotte Moore said: "Drama in 2014 has got off to a great start on BBC One and The Musketeers has really brought something fresh and new to the channel. I can't wait to see how things will develop in the next series."
Adrian Hodges - who adapted the show from the original Alexandre Dumas stories - added that he is "completely thrilled" by the renewal news.
"Writing and helping produce the show has been one of the greatest challenges and joys of my professional life," Hodges said.
The four Musketeers - Luke Pasqualino (D'Artagnan), Tom Burke (Athos), Santiago Cabrera (Aramis) and Howard Charles (Porthos) will all return for the second series.
Further cast details are yet to be announced, though Peter Capaldi will not be reprising his role as Cardinal Richelieu due to his commitments to Doctor Who.
The Musketeers continues tonight with its fourth episode 'The Good Soldier', airing at 9pm on BBC One.
Peter Capaldi perfect for Doctor Who, say Musketeers co-stars