In-House, Contractors, or Partners: Who Should Handle Post-Merger Integration?

You've decided on your integration level. You know what needs to happen. Now the question becomes: who's actually going to do it?

This isn't a trivial decision. The wrong resourcing choice can mean blown timelines, failed migrations, or paying significantly more than you needed to. The right choice depends on your internal capacity, the complexity of what you're integrating, and how much you're willing to spend.

Research from Eight International found that 75% of acquirers achieved their strategic goals when they had a dedicated integration leader, but fewer than 50% of companies actually establish dedicated change management workstreams. There's often a gap between knowing integration matters and actually resourcing it properly.

This article looks at your options honestly: what works, what doesn't, and when each approach makes sense.

This article is adapted from Chapter 3 of The Roll-Up Integration Playbook, our free guide to post-merger technical integration.

Option 1: Your In-House Team

The instinctive first choice is to use the people you already have. Your IT team, your operations staff, maybe the acquired company's systems person.

What Works About In-House

• They know the business. Your team understands how your systems are actually used, not just how they're supposed to work.
• No procurement overhead. You don't need to find, vet, and contract external help.
• Available immediately. No lead time to engage.
• Knowledge stays in-house. Whatever they learn during the integration becomes institutional knowledge.

What Doesn't Work

• Bandwidth constraints. Your IT team is already keeping the lights on. Adding a major integration project means something else doesn't get done, or everything gets done poorly.
• Integration isn't their expertise. Running day-to-day IT operations and executing a complex migration are different skillsets. Your team may be learning on the job.
• They're often wearing multiple hats. The person responsible for integration is also handling support tickets, managing vendors, and a dozen other things.
• The acquired company's "IT person" may be one employee who knows where the passwords are, not someone who can lead a migration.

Research shows that fewer than 20% of organisations improve IT costs and quality post-merger. Part of the reason: internal teams lack the bandwidth and expertise to execute integration well while also maintaining operations.

When In-House Works Well

• Small, straightforward acquisitions with minimal system complexity
• Your team has genuine integration experience (not just operational IT)
• You have dedicated capacity to allocate without degrading other work
• The integration is mostly about configuration, not complex data migration

When It Doesn't

• Complex migrations involving multiple systems
• Tight timelines that require focused, dedicated resources
• Your team lacks experience with the specific platforms involved
• The integration is large enough that it would consume your IT team for months

Option 2: System-Specific Contractors

The next option is to bring in specialists for the systems you're migrating. A Salesforce partner to handle the CRM migration, a NetSuite consultant for the ERP, a Microsoft partner for the email and collaboration move.

What Works About System Contractors

• Deep expertise in their system. They know the destination platform inside and out.
• Established processes and tools. They have migration scripts, testing frameworks, and project templates ready to go.
• Vendor relationships. If something goes wrong, they have escalation paths you don't.

What Doesn't Work

• They're optimised for the destination, not the source. Your Salesforce partner knows Salesforce. But they don't know the five different CRMs you're migrating FROM. They're incentivised to get data into their system, not to untangle the mess on the other end.
• They often skip change management. Technical migration is their core business. Training users, managing resistance, and ensuring adoption is usually not.
• Multiple contractors means multiple relationships. If you need CRM, ERP, and email migrations, you're now managing three separate engagements with three different timelines and no one responsible for the whole picture.
• They don't understand roll-up dynamics. A Salesforce partner helping a single company upgrade is different from helping a platform absorb its fifth acquisition while three more are in the pipeline.

According to Gartner, 83% of data migration projects fail or exceed budget and timelines. Much of this comes from underestimating the source-side complexity, exactly what system contractors tend to de-prioritise.

When System Contractors Work Well

• Single-system migrations where the complexity is in the destination platform
• You have strong internal project management to coordinate across vendors
• The source data is clean and well-structured
• Technical migration is the main challenge (not change management or process alignment)

When They Don't

• Multi-system integrations requiring coordination
• Messy source data that needs significant cleanup before migration
• Change management is a major concern
• You need someone accountable for the overall integration, not just their piece

For more on the technical side of migrations, see System Migration After Acquisition: CRM, ERP, Email, HR, and Operational Tools.

Option 3: Big Consultancy Firms

For larger integrations, you might consider the major consulting firms (Big 4 and similar). They offer comprehensive M&A integration practices with proven methodologies.

What Works About Big Consultancies

• Comprehensive capability. They can handle strategy, execution, and change management under one roof.
• Proven methodologies. They've done hundreds of integrations and have refined playbooks.
• Scalability. If you need 20 people on the ground, they can provide them.
• Credibility with boards. If you need to show your PE sponsor that integration is being handled professionally, a big-name firm provides that assurance.

What Doesn't Work

• Expensive. Day rates of £1,500+ are common. A 90-day integration can easily cost more than the technology itself.
• Often overkill for mid-market. Their methodologies were designed for billion-pound corporate mergers. For a £5M acquisition, you're paying for structure you don't need.
• Junior staff do the work. You buy based on the partner's credentials, but the day-to-day work is done by analysts who may have less experience than your own team.
• May not match the pace required. Large consultancies have processes and governance that can slow things down. Roll-ups often need to move faster and scrappier than big-firm methodology allows.

For context: the PMI consulting market is worth USD 8 billion, growing at 10%+ annually. But much of this serves enterprise mega-mergers. Mid-market roll-ups often find these firms mismatched to their needs.

When Big Consultancies Work Well

• Large, complex integrations with significant risk
• Multiple simultaneous acquisitions requiring coordinated programme management
• Board or investor requirements for external validation
• Budget is less of a constraint than risk mitigation

When They Don't

• Mid-market acquisitions where the integration budget needs to be proportionate
• Situations requiring speed and flexibility over process rigour
• When you need hands-on execution, not frameworks and recommendations

Option 4: The Integration Partner Model

There's a gap between system contractors and big consultancies that few firms specifically address.

The mid-market roll-up (doing 2-10 acquisitions per year, needing real integration work but not enterprise budgets) often ends up either stretching internal teams beyond capacity, or stitching together multiple contractors with no one owning the outcome.

What an Integration Partner Looks Like

• Platform-agnostic. Not tied to a single system, so they're not optimising for one destination at the expense of understanding the source chaos.
• Owns the overall outcome. Accountable for the whole integration, not just one system or one phase.
• Right-sized for mid-market. Not delivering 200-page strategy decks when you need a working CRM migration.
• Understands both sides. Comfortable working backwards from messy source systems, not just forwards into clean destinations.
• Change management as core. Treats training and adoption as part of the work, not an afterthought.

This model works well when you need more than a system contractor but less than a full consulting engagement. You get dedicated expertise without building permanent headcount, and someone accountable for the whole picture rather than just their piece.

For more on why change management matters, see Why Systems Don't Fail — Adoption Fails.

Questions to Guide Your Decision

Regardless of which option you choose, here are the questions to ask yourself:

Capacity & Expertise

• Do we have internal capacity to dedicate to integration without degrading other work?
• Does our team have genuine experience with the migrations we're planning?

Complexity & Scope

• How many systems are involved?
• Is the integration primarily technical, or is change management a major factor?
• Do we need someone accountable for the whole picture?

Budget & Timeline

• What's our budget relative to the complexity?
• How tight is the timeline, and what happens if we slip?

Strategic Context

• Is this a one-time integration, or the start of an ongoing acquisition programme?
• How important is building internal capability vs. getting this done fast?

For a structured framework to work through these questions, see Post-Merger Integration Checklists and Templates.

A Quick Comparison

In-HouseSystem ContractorsBig ConsultancyIntegration PartnerBest forSimple integrationsSingle-system migrationsEnterprise/complexMid-market roll-upsCostStaff time£500-1,000/day£1,500+/day£500-1,000/dayExpertiseKnows your businessKnows destination systemBroad methodologyCross-platform, PMI-specificAccountabilityYou own itTheir system onlyFull (at a price)FullChange managementUsually internalUsually notIncluded (expensive)Core to offeringScales with acquisitionsLimitedPer-projectYesYes

Key Takeaways

• In-house works for simple integrations where you have genuine capacity and expertise. It struggles with complex migrations or tight timelines.
• System contractors bring deep platform expertise but are optimised for their destination system, not the source chaos. They work best for single-system migrations with strong internal coordination.
• Big consultancies offer comprehensive capability but at a price point and pace that often doesn't fit mid-market roll-ups.
• The integration partner model fills the gap for mid-market serial acquirers who need dedicated expertise without enterprise overhead.
• The right choice depends on your situation. There's no universally correct answer. Match your resourcing to your complexity, timeline, and budget.

Get the Full Playbook

This article covered your options for getting integration done. For the complete guide, including the integration audit process, 100-day execution timeline, and ready-to-use checklists, download The Roll-Up Integration Playbook.

Download the Playbook

About PMI Stack

PMI Stack is a technical integration partner built specifically for small-to-mid cap roll-ups. We help companies unify systems, data, and workflows across their acquired companies, handling the technical migration and the change management that makes new tools stick.

If you're planning an integration and want to explore whether this approach fits your situation, book a free discovery call.

Statistics cited from Eight International, Gartner, and Verified Market Research. For the full research compilation, see 50+ Post-Merger Integration Statistics (2026).