Whether it's to welcome a new baby or to celebrate an engagement or another occasion for congratulations, throwing a surprise party can be a fun way to share an exciting event. Hosting a surprise congratulations party may require some additional work, though, since you and all of the guests have to keep the details secret from the guests of honor the entire time you're planning it.
Make a guest list. Creating a guest list may be tricky with a surprise congratulations party because you won't be able to ask the guest or guests of honor who they want to invite. Contact family, friends and co-workers to get the names, addresses and other contact information for people on your party invite list.
Pick an accessible location. When throwing a surprise party, the location of the party should be easily accessible for most attendees and one that you can somehow persuade the guest of honor to come to on the day of the party. This may mean holding the surprise party at your own home or renting a room in a restaurant so you can lure the person there under false pretenses.
Create a way to bring the guests of honor to the party. In order for them to actually arrive to the party, you need to make up an excuse for them to come to the party location. Ideas to consider include going to your house for a family dinner, to a cafe for a girls' night out, or to the movies, beach, mall, or museum. Be sure to make the "fake" event at least a few hours long, so that you know their whole night is clear.
Choose a party date. By creating a way to get together with the guests of honor, you can also choose a date for the party. Check on her work schedule and other commitments with friends, family members and co-workers to choose a date and time when you know she is available. If you know she has a work meeting every Friday that lasts until four, offer to pick her up after the meeting to go to dinner or grab drinks to celebrate her recent promotion or reason for congratulations. Since you now know of a time that she'll have blocked off from other commitments, you can utilize this time period for the party.
Make invitation, food and beverage arrangements. Once you have all of these arrangements made, you need to send out the party invitations and request an RSVP to ensure you have enough food and beverages for the party. Order or make the food and beverage arrangements based on slightly more people than are expected to attend to be sure you won't run out of anything.
Buy congratulations party supplies. Buy and decorate the surprise party room with banner, balloons and cutouts that say "surprise" and "congratulations." For an added effect, give party guests noisemakers or confetti to use when the guest of honor walks into the room and everyone jumps out and says, "Surprise!"