Underlying earnings (EBITDA) excluding acquisition and other exceptional costs rose 24 per cent to £1.2m on revenue up nine per cent to £19.4m; Porta said growth was entirely organic because there were no acquisitions.
The company said gross profit was 25 per cent higher in its PR and communications offering, which accounted for £18m of revenue in the period and consists of Newgate Communications, Publicasity and Redleaf Communications. Most of that growth has come from Asia-Pacific, where gross profit rose 58 per cent.
In addition to PR and comms, the group has marketing, design and advertising companies.
The results follow a period of change at the listed group, which last month agreed to sell a 19.3 per cent stake to Italian PR firm SEC for £3m and to work together on joint business opportunities.
In May, executive chairman David Wright retired and stepped down from his role, prompting a reshuffle of senior positions. His role was filled by John Foley, previously a senior independent non-executive director.
Also in May, Porta reported a nine per cent rise in revenue to £37.1m in 2016, although earnings fell, with the firm citing investments at Newgate and a Brexit-related slowdown at PPS.
The period also saw the completion of the integration of public affairs firm PPS into sister agency Newgate Communications.
Steffan Williams, Porta CEO, said: "Porta is in the next phase of its development. In addition to the solid first half performance and the successful ongoing strengthening of our balance sheet, we have made a number of changes to the board and management team which are having a positive effect on the performance of the business.
"The group is trading ahead of last year and we look forward to building on the strong progress made in the first half."