Ramsay signed for a closing 68 at the last full-field event of the season to jump up to 115th in the Race to Dubai Rankings presented by Rolex and retain his European Tour card.
Seven-time winner Gonzalo Fernández-Castaño also did enough to keep his card for next season, finishing in a tie for fifth on four under par to move from 125th in the rankings to 104th.
England's David Horsey, who had started the tournament in 116th place, clinched the final spot after finishing two over par for the week.
Scotsman Ramsay began the week in an unfamiliar position, sitting 124th in the rankings, knowing a big week would be required in Spain to get inside the top 116.
And he started well, producing an opening 69 on Thursday before the event was hit by a series of weather delays and eventually reduced to 54 holes.
A second-round 74 gave Ramsay work to do in the final round and he rose to the challenge, carding three birdies and one bogey in his first 12 holes on Sunday before more inclement weather forced play to be suspended until Monday morning.
And when the action resumed, the three-time European Tour winner fired another birdie at the 13th before parring his way home to finish in a tie for 11th on two under.
Ramsay said: "I didn't sleep the best but I think I came out and proved a lot to myself, arguably under the most pressure I’ve ever felt coming down the stretch, but it’s a course I love which made it far easier to go out there and play.
"I had some good looks at some great putts on 16 and 17 and then I rolled in a nice little tester at the end from about three feet. A three-footer under normal circumstances is very easy, but not when your job is on the line.
"I'm just proud of the way I played."
Fernández-Castaño followed up opening rounds of 70 and 68 with a closing 71 on Monday to secure his card and he was thrilled with his week's work.
He said: "I did it, I did it!
"It’s been such a long week, so many sleepless nights – and the pressure today.
"Yesterday I was surprisingly calm but last night I could hardly sleep and this morning I was pretty nervous - I knew what was at stake.
"I’m really, really happy and also quite proud of what I’ve done this week, when I needed to deliver I did, so I’m excited.
"If I had to choose a tournament to keep my card it’s probably this one. It doesn’t particularly suit my game but it’s a course I know very well and also I knew the scoring would not be extremely low.
"I like courses where pars are good and that’s what Valderrama is about.
"I’m very excited to be back with full status on the European Tour.
"I believe I still have a few years ahead to win tournaments, and hopefully 2019 will be one of them."