Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) says that a marriage takes place in the presence of four: 1. the guardian, 2. two witnesses, 3. the one marrying.
It has a supporting report from Ibn Abbas with a munqati' (broken) chain.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13814