The 30-year-old has been sidelined since a hip injury forced him to withdraw from the Australian Open in January.
Confirmation of Nadal's return came on Thursday afternoon at the draw for the Davis Cup quarter-finals.
Spain host Germany in Valencia on Nadal's favoured clay surface and the 16-time grand slam winner will face Philipp Kohlschreiber in the second rubber after David Ferrer takes on Alexander Zverev.
Nadal, who has won his past 22 singles rubbers, will then face world No.4 Zverev in the first match on Sunday.
Despite his spell on the sidelines, Nadal reclaimed the top ranking after Roger Federer's surprise loss to Australia's world No.175 175 Thanasi Kokkinakis at the recent Miami Open.
Nadal has not lost a singles rubber since his debut in the competition when Jiri Novak of the Czech Republic beat the then 17-year-old in 2004.
