In this sentencing, "to helping" means the act of helping. In this case, it is not a verb, but an object for the sentence. You can also use the verb "to help:" "He was a man who devoted his whole life to help his people."

Don't make the mistake of thinking that 'to' is always followed by the base form of the verb ( to help, to go, etc). In fact, 'to' is only followed by this form when it is part of the infinitive, as in 'I want to do' , 'I need to do', 'I hope to do' and so on. If 'to' is part of a phrasal verb, prepositional verb or another verb phrase, such as 'to be used to' 'to look forward to' 'to be addicted to' 'to be opposed to', it needs to be followed by a gerund (the 'ing' form). For example : I'm looking forward to meeting you. I'm not used to speaking in English are both very common used of 'to' followed by a gerund. Prepositions ( of, from, with etc) are always followed by nouns or gerunds. A gerund is a verb doing the job of a noun. So, just as you would say 'He devoted his life to his family' or 'He devoted his life to his studies' (nouns) , you say 'He devoted his life to helping..'