大成功だった

was a great success

→ 大成功
phrase Rare #20,558
was a great success 大成功 means “great success,” and だった is the past form of だ, meaning “was.” The polite equivalent is 大成功でした.
JA: 昨日の発表は大成功だった。
EN: Yesterday's presentation was a great success.

その映画は大成功だった

That movie was a huge success.

パーティーは大成功だった

The party was a huge success.

天気が良かったのでその野外コンサートは大成功だった

The outdoor concert was a great success because the weather was good.

大成功だった

It was a huge success.

我々の交渉失敗どころか大成功だった

Far from being a failure, our negotiations were a resounding success.