Hi Rajashri,

check this one, looking for try eradicate the duplicates

<apex:page StandardController="Campaign"  extensions="CampaignMemController">
    <apex:form >
        <apex:pageBlock title="Campaign Members Details" mode="maindetail">
            <apex:pageBlockSection title="Campaign Members"  id="cm3">
                 <apex:pageblocktable value="{!cm}" var="lead">
                        <apex:column headerValue="Name">
                            <apex:outputfield value="{!lead.name}" />
                        </apex:column>
    
               </apex:pageblocktable>   
            </apex:pageBlockSection>
        </apex:pageBlock>
    </apex:form>
</apex:page>


public with sharing class CampaignMemController {

    public Campaign camp {get; set; }
    list<contact> con = [SELECT id,name FROM contact];
    public List<contact> cm {get; set;}
    list<campaignmember> cmlist = [SELECT id, contactid FROM campaignmember];
    list<contact> conlist = new list<contact>();
    
     public CampaignMemController(ApexPages.StandardController controller) {
         camp  = (Campaign)controller.getRecord();
 
 
        for(campaignmember cm : cmlist)
        {
             for(contact c : con)
            {
                     if(c.id == cm.contactid){
                         conlist.add(c);
                     }
             }
    

        }  
        cm =conlist;
        System.debug('All the campaignmemebers under contact '+conlist+'are');
        System.debug('Test value of CM'+cm);
         
        
    }

}