Here are well-known Colombo hotels that offer large event/conference spaces (ballrooms, convention halls, lawns) suitable for conferences, large banquets, exhibitions or weddings — with key capacity/space notes and links to their event pages.

1. ITC Ratnadipa, a Luxury Collection Hotel (Colombo) — Sangam Ballroom

• Largest event capacity: up to about 1,600 (theatre). Total meeting space ~3,178 sq. m; largest single ballroom for large conferences and banquets. (marriott.com)

2. Hilton Colombo / Hilton Colombo Residences — Union / Grand ballrooms

• Pillar‑free large ballroom options. Union Ballroom (Hilton Colombo Residences) holds ~1,100 theatre; total event space over 1,100–1,300 sq. m depending on configuration. Good AV and direct downtown access. (Hilton.com)

3. Shangri‑La, Colombo

• Large modern ballrooms and flexible meeting rooms for high‑end conferences and gala events (sizable capacities for large gatherings; full specs on the hotel events page). (brandradar.org)

4. Cinnamon Grand Colombo — Oak Room & other ballrooms

• The Oak Room (Cinnamon Grand) is a large, flexible ballroom used for conferences/weddings — several hundred guests (conference/banquet setups quoted in hotel materials; can be subdivided). (yumpu.com)

5. Cinnamon Lakeside / Cinnamon Life (Cinnamon Life Integrated Resort)

• Cinnamon Lakeside and the new Cinnamon Life integrated resort include very large meeting/exhibit facilities and ballrooms — suitable where you need exhibition halls and very large plenary capacity. (Cinnamon Life is a major MICE development in Colombo.) (brandradar.org)

6. Taj Samudra, Colombo

• Established hotel with large ballrooms and lawns for banquets, conferences and marquee events — commonly used for large gatherings and seaside events. (brandradar.org)

7. The Kingsbury Colombo

• Harbour‑front hotel with flexible ballrooms and function rooms for several hundred guests; suitable for banquets, conferences and waterfront receptions. (brandradar.org)

8. Mount Lavinia Hotel (near Colombo)

• Historic seafront hotel offering large ballrooms and lawns that can host several hundred guests (popular for weddings and large banquets). (venues.lk)

9. Courtyard by Marriott Colombo

• Modern event spaces with a largest room capacity around 300 and ~917 sq. m total event space — good for mid‑large conferences and breakout rooms. (marriott.com)

Notes and next steps

• Capacities vary by setup (theatre, banquet, classroom) and whether ballrooms are used whole or partitioned — always confirm the exact seating layout, AV needs and COVID/safety rules with the hotel’s events team.
• If you want, I can:
  • Narrow these to a short list based on a target guest count (e.g., 300 / 600 / 1,200), budget, preferred neighborhood (Galle Face / Fort / Union Place / Cinnamon Gardens), or date.
  • Pull floor plans, ballroom dimensions and direct contact/email for the events teams and attach/compare capacities by seating style.
  • Request proposals / availability from 3–4 hotels on your behalf (you’ll need to give dates and estimated guest count).

Which of the above would you like to explore further — or tell me your expected guest count and preferred area and I’ll shortlist best matches with floorplans and contact details.