Last night's event was sponsored by CitiBank, Belfast's biggest employer.
Mr Houston praised DUP leader Arlene Foster for her attendance.
"It's brilliant and to be commended that Arlene Foster is to attend," he said.
Mr Houston said he believed big companies were now committed to welcoming a diverse workforce, including gay people.
"From the trade unions to the banks, the big accountancy firms and big law firms - I can think of no other issue or movement which has attracted such a rainbow - pardon the pun - of groups and organisations. Businesses are on to the fact that the wider issue of diversity and equality equals business success."
But he said that same-sex marriage should be brought into force in Northern Ireland.
"To me, equal marriage is a symbol of the kind of society we are.
"We need the message that when you grow up, you can marry whoever you happen to love. It's totally unacceptable for some citizens here in NI to be second-class citizens, in that they are unable to marry their partner."
While PinkNews said there would be business people in attendance, it's understood Northern Ireland's main business groups - Retail NI, the NI Chamber of Commerce and Industry, the Institute of Directors and CBI - were not invited.
Cai Wilshaw from PinkNews said: "Many businesses have elected to send employees involved in their LGBT networks. We have representatives from major retail banks, law firms, IT firms and smaller businesses."
Glyn Roberts, chief executive of Retail NI, said: "We want to see Northern Ireland becoming the very best place in these islands to shop, socialise, start or locate a business. To achieve that, we must have a society which is welcoming, tolerant and respectful to everyone.
"In that regard, the issue of civic equal marriage needs to be addressed by an incoming Executive."