The Hammers have struggled in the early stages of the new Premier League season, losing their opening three games without scoring, but they have had no problems finding the net in Europe as they netted three goals in both legs against their Danish counterparts.
Leading 3-1 from last week's first leg at the London Stadium, West Ham extended their advantage on aggregate through summer signing Gianluca Scamacca, who flicked the ball in at the near post in the 22nd minute.
Said Benrahma ran in behind and fired past Viborg goalkeeper Lucas Lund Pedersen to double the visitors' lead on the night six minutes after the break, before Tomas Soucek added a third just after the hour mark with a simple finish inside the six-yard box.
David Moyes's men will find out who they will face in the Europa Conference League group stage when the draw is made at 14:30pm (CET) on Friday in Istanbul.
Speaking to reporters after the match, Moyes said: "It is a special thing being in Europe and what makes it really special is that you don't get it very often.
"You can sometimes find people who treat it with a bit of disrespect, but I wanted to make sure we treat it with great respect because I want us to try and do well and compete in it. Now we've got another period of European football and playing games in places we've maybe not done before, so we look forward to it.
"The only way you get in Europe is if you do well in your domestic league, so we've done well in our domestic league the last couple of years. That got us in it, and I want to try and do well in it.
"We tried really hard last year and we had a great run in it and now we'll obviously try and do the same in this competition."
West Ham, who reached the Europa League semi-finals last season, will now turn their attention back to the Premier League with a trip to Aston Villa on Sunday.