Maldonado said: "For sure I will try to win. It is a pleasure to be part of Williams, which is a legendary team.
Hamilton delighted with 'best ever' pole
"I have a mission to take them back to the top of the grid."
Maldonado acknowledged he was facing a powerful rival in double world champion Fernando Alonso, who starts second in his Ferrari.
"The gap is very close and Alonso is a tough one, it will be a wonderful race to see," Maldonado said.
The 25-year-old owes his position at Williams to financial backing from his home nation's state oil company.
He said: "I think everyone in Venezuela is very happy and I am very happy to be part of them.
"It is a real pleasure to have a country pushing very hard to have me doing well in Formula 1."
Lotus drivers Romain Grosjean and Kimi Raikkonen, who were very strong in their race-simulation runs on Friday, will start third and fourth, ahead of Sauber's Sergio Perez and Mercedes driver Nico Rosberg.
David CoulthardBBC F1 co-commentator
"Are we in a time now when the tyres are so critical that no-one pushes for grid position in qualifying and everyone just concentrates on the 66 laps of the race instead?"
Red Bull's world champion Sebastian Vettel qualified only eighth - and is now seventh on the grid.
Vettel was so far down because he had used up all his 'soft' tyres in getting through to the top-10 shoot-out.
He said: "We didn't have the pace of the top five cars today. Tyres will be important tomorrow, so let's see what we can do."
The fact that he was struggling for pace despite looking fast throughout practice underlined what a topsy-turvy race weekend this is turning out to be.
McLaren's Jenson Button and Vettel's Red Bull team-mate Mark Webber were 11th and 12th.
They missed out for different reasons - Button was struggling with the handling of his car and Webber because the team erroneously thought his first lap would be quick enough to get him through.
Instead, as others improved, Webber slipped out of the top 10 - the agony of his situation was underlined by the fact that there was just 0.121secs between his time and that of Raikkonen, who was fifth in the second session.
Team boss Christian Horner said: "We thought we'd just done enough."
Red Bull trio reflect on difficult session
Button had been fastest in Friday practice but found his car transformed from the start of Saturday.
He said: "I don't know (where it went wrong). All day I have struggled with the balance, yesterday the car was fantastic, I thought we'd be quick enough today, at least get into Q3. I've struggled with a very different balance.
"Then in qualifying I struggled with oversteer and then when I added more front end I had understeer. I don't know what's going on.
"The speed's in the car I just don't know what's going on with mine."
Force India's Paul di Resta was 13th, just ahead of team-mate Nico Hulkenberg.
Alonso, who was driving a car with a large number of upgrades, added: "We did a step forward, I don't know how much because I think P3 is over-performing.
"I was really happy with the lap, it was perfect, I could fit 100 more sets of tyres and not do better."
Maldonado's impressive qualifying performance was by far the best result of his career, and it underlines Williams's return to form this season after a number of difficult seasons.
"We have been working so hard trying to understand these tyres and to develop our car around these tyres," Maldonado said.
"We did a very good step forward for this race. There is a great atmosphere in the factory and team. The car looks fantastic especially on race pace."
Spanish Grand Prix 2012, Circuit de Catalunya, day three
Sunday 13 May: Race 12:10 BST BBC One and BBC One HD, BBC Radio 5 live and live text commentary on BBC Sport website; Highlights 19:00-20:00 BST, BBC Three
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