Williamson said it was important to share grief when tragedies like this happen that affects the entire country.
"This is not what we expect in New Zealand," she said.
The Mayor will address those at the vigil and other authorities from different churches will lead prayers.
Hymns will be sung as well as the national anthem before an opportunity to light a candle.
People will also be invited to write a message on a prayer wall, which will be left at the Tauranga Mosque as a tribute.
Other vigils were also held over the weekend at Tauranga's Yatton Park, Mount Maunganui Main Beach and Te Puke's Jubilee Park, where hundreds of people turned up to pay tribute.
The Mayor said he had been touched by the amount of support the city had shown for the Muslim community by leaving tributes at the local Mosque and organising vigils.
Brownless attended the vigils at Yatton Park and Mount Maunganui over the weekend and planned to attend the combined church prayer at Holy Trinity Church this evening.
"They [the vigils] have been so spontaneous and heartwarming," he said.
Tauranga vigil:
What: Combined Churches Prayer Vigil
Where: Holy Trinity Church, 215 Devonport Rd
When: March 18, 7pm