The Strategic Role of an In-House Mobility Tax Advisor

There is a saying in the UK that when two similar things happen in quick succession, it’s like London buses: you wait for ages and then two come along at once! In this case, the London buses are in fact two identical questions. They came from two very different clients within a few days of each other, and the question was about the role of an in-house tax expert.

In both cases, I’ve been working on large-scale mobility programme modernisation projects. I love these projects because they are so wide-ranging and touch on every aspect of the function. And the question? Both companies wanted to know whether they should have an internal global mobility tax expert embedded in their team, what other companies are doing, and the associated advantages and disadvantages.

What does the benchmark data say?

In all honesty, I had no idea! We don’t have specific benchmark information on this. But the joy of working at AIRINC is that there are ways to find out. I discussed it with our Tax Team to get their perspective; they have a wealth of practical knowledge as well as tax technical expertise. They said they see a bit of everything! We did a straw poll of around 20 clients from similar industries and with similar-sized programmes — around 500 assignees — and within a few days, we had a decent understanding of the market position.

What we found was both illuminating and very unhelpful! Across the clients and industries, there was a very even split between those companies with internal global mobility tax expertise and those without. This wasn’t helpful in terms of giving the clients a clear yes or no answer. However, it was illuminating because, if the market is so evenly split, other factors must be influencing the decision.

Understanding the drivers for and against an internal tax resource is essential for a company deciding what is right for them, based on culture, cost, risk profile, vendor leverage model, internal networks, and more. Let’s dig into this a little further.

Why Global Mobility Programmes Are Rethinking Tax Expertise

As global mobility programmes become more complex, organisations — like my two “London buses” — are re-evaluating how they manage tax planning, compliance, and cost control. Traditionally, many companies have relied heavily on external tax providers to manage cross-border employee taxation. However, a growing number are exploring the addition of an in-house Mobility Tax Advisor to strengthen both operational efficiency and strategic oversight.

This role goes far beyond compliance. It sits at the intersection of mobility, finance, payroll, and corporate tax, helping organisations make smarter, more integrated decisions

What Does an In-House Mobility Tax Advisor Do?

We interviewed a number of our clients to understand the typical responsibilities of an in-house tax expert. Not every company defines the role in the same way, but there were a number of areas that overlapped across many organisations.

1. Drives Smarter Tax Planning for Assignments

An in-house tax advisor can bring a deeper understanding of the organisation’s mobility programme, enabling more tailored and proactive tax planning.

They help:

• Evaluate the most tax-efficient assignment structures, such as host-based and local-plus approaches

• Design and apply allowances and benefits with tax efficiency in mind

• Support both individual assignments and broader policy development

Rather than reacting to tax implications after decisions are made, organisations can build tax efficiency into the design of every assignment.

2. Acts as a Critical Liaison Across Functions

Mobility leaders commented that one of the most valuable — and often overlooked — benefits of this role is its ability to bridge internal silos. Specifically, they mentioned that an in-house advisor:

• Translates between mobility, payroll, finance, and corporate tax teams

• Aligns stakeholders with competing priorities, including cost, compliance, and employee experience

• Improves communication with external tax vendors

This results in clearer questions, faster responses, and fewer costly misunderstandings with external providers.

3. Reduces Reliance on External Tax Providers

External advisors remain essential, especially for jurisdiction-specific expertise. However, an internal tax expert can significantly optimise how those external resources are used. For example, they can:

• Filter and refine queries before sending them to vendors

• Provide Tier 1 tax advice

• Reduce back-and-forth communication and significantly speed up the acquisition of relevant, actionable tax advice

GM leaders with a tax manager role in their team also mentioned that external consulting fees can decrease substantially, sometimes offsetting the cost of the in-house role.

4. Improves Tax Equalisation (TEQ) Processes and Cost Recovery

Although potentially not the most glamorous role (!), an in-house advisor can:

• Review and validate tax provider calculations

• Ensure collections of employee balances are completed

• Manage employee questions and disputes internally

This hands-on oversight helps accelerate collection, recover funds that might otherwise be lost, and reduce reliance on expensive external dispute resolution.

5. Enhances Governance and Compliance

With a dedicated expert focused on mobility tax, organisations gain stronger oversight and accountability. This comes through:

• Improved compliance tracking and documentation

• Consistent governance of tax processes

• Better risk visibility across mobility programmes

The result is not just cost savings, but greater programme integrity and control.

Cost Considerations and ROI

One of the most common concerns is cost. However, many organisations find that this role can effectively pay for itself through:

• Reduced external consulting spend

• Improved tax efficiency in assignment design

• Better recovery of tax equalisation payments

The other main challenge cited by mobility leaders is headcount. Often, there simply isn’t the capacity to add a tax manager to the function. Some companies address this by cooperating with the corporate tax or finance functions. Headcount may actually sit outside the GM team, while the tax manager maintains a strong liaison role with GM.

We also saw examples where headcount costs were allocated across mobility, finance, and corporate tax, or where costs were charged out to the business to help fund the role.

When Does an In-House Role Make Sense?

The upshot of the research we did for these clients is that the value of an in-house Mobility Tax Advisor depends largely on:

• Programme complexity, including varied assignment types and multiple jurisdictions

• Volume of mobility activity

• Reliance on external consulting spend

• Organisational risk appetite

• The balance between standardisation and customisation

• Vendor leverage model

Large, complex programmes often benefit most, but even smaller, highly customised programmes can justify the role.

From Compliance to Strategic Advantage

Ultimately, the in-house Mobility Tax Advisor represents a shift in mindset: from treating tax as a compliance requirement to leveraging it as a strategic enabler.

By embedding tax expertise within the business, organisations can:

• Make faster, more informed decisions

• Improve cross-functional alignment

• Unlock meaningful cost savings

In today’s global environment, that’s not just an operational improvement; it’s a competitive advantage.

If you’re thinking about tax, or any other aspect of mobility programme modernisation, AIRINC can help you assess the options, benchmark against peer organisations, and identify the right approach for your organisation.