Greece has the European national anthem associated with the greatest number of verses: its “Hymn to Liberty” poem contains 158 four-line stanzas. The poem was written by Dionysios Solomos in 1823 during the Greek War of Independence.
The unusually long work is not performed in full. The Greek national anthem uses the first two stanzas, while the first 24 stanzas were designated for official anthem use when the hymn was adopted in 1865. The complete 158-stanza poem is therefore the source of the record-like trivia fact, even though ceremonies use only a tiny portion of it.
Music for the poem was composed by Nikolaos Mantzaros. The march-like version gained official status after the union of the Ionian Islands with Greece, and the anthem was formally adopted in 1865. The same anthem is also used by Cyprus.
A common mix-up is to say that Greece has a 158-verse song played at every ceremony. In practice, performances are short: normally the first two stanzas are sung or played. The distinction between the full poem and the performed anthem explains the qualification behind this answer.