The teams were tentative on the soggy track, with most delaying sending their drivers out due to the wet conditions, while Force India's James Rossiter decided against taking part in practice one because of the weather.
Sauber's Esteban Gutierrez and Red Bull's Sebastian Vettel emerged onto the Silverstone circuit for a cautious drive around the track, but it was Ricciardo who completed the first timed lap 77 minutes into the session.
After clocking the time of 1:54.249, Lewis Hamilton entered the track, which contained puddles of standing water, for Mercedes but could only muster a time of 1:55.458.
First practice standings of 11 drivers:
1. Daniel Ricciardo (Toro Rosso)
2. Niko Hulkenberg (Sauber)
3. Pastor Maldonado (Williams)
4. Lewis Hamilton (Mercedes)
5. Esteban Gutierrez (Sauber)
6. Valtteri Bottas (Williams)
7. Jean-Eric Vergne (Toro Rosso)
8. Giedo van der Garde (Caterham)
9. Max Chilton (Marussia)
10. Jules Bianchi (Marussia)
11. Felipe Massa (Ferrari)