Sync Mailchimp and HubSpot

What This Integration Does

This integration keeps contact data in step between Mailchimp audiences and HubSpot CRM as a true bi-directional sync. Contacts created in either platform appear in the other with the agreed field mapping. List or audience membership changes propagate. Engagement events from Mailchimp flow into HubSpot as timeline activity. Unsubscribes in either system flow to both. It is one of the system-to-system sync integrations we build for teams that have outgrown a packaged connector.

It exists because the off-the-shelf Mailchimp-HubSpot connector handles the basics but leaves gaps that compound at scale. Custom fields go missing, list membership drifts, and unsubscribe latency creates compliance risk.

The Workflow

The sync engine watches both platforms continuously. A contact created in HubSpot, usually through a form fill, sales rep entry, or list import, appears in the matched Mailchimp audience within a minute with the agreed field set populated. A contact added to a Mailchimp audience via a Mailchimp-hosted signup form appears in HubSpot as a new Contact with lifecycle stage set and a custom property identifying the source audience.

Field-level sync rules manage conflict. For each field, one platform is the authority. HubSpot owns lifecycle stage, lead status, and CRM properties; Mailchimp owns email subscription preferences, engagement rates, and audience-specific tags. When a value changes in the authoritative platform, it overwrites the other. When a value changes in the non-authoritative platform, the change is rolled back to maintain consistency.

Take one specific chain. A contact unsubscribes from a Mailchimp audience by clicking the unsubscribe link in a newsletter. Within seconds, the integration writes the unsubscribe to HubSpot. The contact’s marketing email subscription is set to opted out, the timeline shows the unsubscribe with the source campaign, and any active workflows that would have sent marketing email are paused. The sales team sees the unsubscribe on the next view of the contact. No regulated email is sent in the meantime.

Engagement also flows through. Opens, clicks, and bounces from Mailchimp campaigns post as HubSpot timeline events with the campaign name and content, so the sales team sees marketing engagement on the contact record.

Before and After

Before, contacts in HubSpot and Mailchimp drift apart within weeks. Some are duplicated. Unsubscribes from Mailchimp reach HubSpot via batch sync that runs overnight, creating a window where marketing email could still send. Engagement reports live in Mailchimp and never make it back to the sales view.

After, the two systems behave like one contact database. Sales sees marketing engagement. Marketing trusts that lifecycle stages and lead status reflect sales reality. Unsubscribes propagate within seconds, closing the compliance window.

Who Needs This

Mid-market businesses running serious Mailchimp programmes alongside HubSpot CRM, where the volume of contacts and the cost of drift between the two systems makes the standard connector insufficient. The trigger is usually a compliance incident, a sales-marketing alignment exercise, or a list import that exposed how stale the data was. The same drift shows up on other stacks, which is why we also build Klaviyo to HubSpot and Salesforce to Stripe syncs for teams running a different mix of tools.

How We Build This

We build this as a bi-directional sync engine against the Mailchimp Marketing API and the HubSpot CRM API, with last-modified timestamps preventing loops and configured field authority resolving conflicts. The engine runs continuously with webhook subscriptions where available and short-poll fallback where not. See HubSpot API Integration and Mailchimp API Integration for the underlying capabilities.

Get Mailchimp and HubSpot in Sync

If your Mailchimp audiences and your HubSpot CRM are drifting apart and the cost is starting to show, we can build a custom bi-directional sync that keeps the two in step.